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This chapter describes how to configure the Serial Line Internet Protocol (SLIP) on the communication server. You will find the following information in this chapter:
Making SLIP connections is described in the "User Commands" chapter.
The commands to define the configuration are entered in configuration mode, which is privileged. To enter configuration mode, type the configure command at the EXEC prompt. You can then enter the commands described in this chapter. For more information about the configuration mode, see "The Configure Command" in the "Startup and Basic Configuration" chapter.
A command summary is included at the end of the chapter.
The Serial Line Internet Protocol (SLIP) is an inexpensive way of connecting PCs to a network. SLIP can be used over asynchronous dial-up modems, allowing a home computer to be connected to a network without the cost of a leased line. Dial-up SLIP links can also be used for remote sites that need only occasional or backup connectivity. Both public-domain and vendor-supported SLIP implementations are available for a variety of computer applications.
SLIP defines a method of sending Internet packets over standard RS-232 asynchronous serial lines. It is a de facto standard, commonly used for point-to-point serial connections running TCP/IP. SLIP is commonly used on dialup asynchronous serial links with line speeds between 1,200 and 19,200 baud.
The version of SLIP described in this publication was originally implemented by researchers at the University of California at Berkeley in their 4.2 BSD version of the UNIX operating system. Although variants have been proposed, the Berkeley version has emerged as a de facto standard. Refer to RFC1055 for more information about SLIP.
Your communication server supports IP routing connections. If you are connecting a single device to a network, you will not need to implement routing. If you are connecting a network to another network, you will use a configuration that supports routing. The configuration of an interface can be changed at any time to enable or disable IP routing. Compressed SLIP (CSLIP) is also supported, providing faster data transmission across low-bandwidth asynchronous lines.
Figure 1-1 illustrates a typical terminal-connection SLIP configuration.
Figure 1-2 illustrates a SLIP configuration using IP routing.
In addition to implementing the de facto standard, SLIP offers both dedicated and dynamic address assignment, configurable hold queue and IP packet sizes, extended BootP requests, and permit/deny conditions for controlling access to the line.
The Cisco Systems communication servers recognize a variety of Internet broadcast addresses. When a communication server receives an Internet packet with one of these addresses from a SLIP client, it rebroadcasts the packet onto the network without changing the Internet header. The communication server does not alter the packet's broadcast address to match the form of broadcast address it prefers.
The communication server receives a copy of SLIP client broadcasts, and responds to BootP requests with the Internet address of the line that received them. This facility allows the SLIP client software to automatically determine its own Internet address.
Following are the basic steps for configuring SLIP on your communication server:
Step 1: Enable SLIP on an interface by using the slip dedicated, slip address, or slip address dynamic line subcommands.
Step 2: Implement slip routing if required.
Step 3: Make the appropriate settings for the line. Line settings include baud rate, flow control, stop bits, and modem control. These settings are described in the sections "Configuring Asynchronous Lines" and "Configuring the Modem Control Lines" in the "System Configuration" chapter.
Step 4: Optimize SLIP operation as necessary. Options include header compression, unnumbered IP addresses, and definable hold queue and packet sizes.
Step 5: Specify access lists for control of traffic to or from a SLIP-enabled line, if needed.
Step 6: Specify extended BootP requests, if needed.
The following sections describe these step in greater detail. Descriptions of the EXEC commands used to monitor and maintain a SLIP link follow these sections.
You can use one of two EXEC commands to make a SLIP connection, depending on how the line is configured:
slip slip defaultIt is also possible to configure a dedicated SLIP line, in which case no EXEC command is required to make the connections. See Chapter 3, "User Commands," for more information about SLIP EXEC commands.
The following paragraphs describe the ways in which the SLIP lines can be configured.
You can be permanently configure a line for SLIP using the slip dedicated and slip address line configuration commands. Once the physical connection to the line is made, the user is immediately placed in SLIP mode. No prompt or message is issued. Automatic dialing can be implemented across dedicated SLIP lines. See the "System Configuration" chapter for more information about automatic dialing using DTR.
Assign a permanent SLIP address to a line with the slip address line configuration command. In this case, the user issues the slip EXEC command to put the line into SLIP mode. If the server has been configured to authenticate SLIP connections, the user is prompted for a password before the line is placed in SLIP mode.
You can configure a line for dynamic assignment of SLIP addresses with the slip address dynamic command. In this case, the user enters the slip EXEC command and is prompted for the IP address or logical host name. If the address is on the local Ethernet, routing is not implemented. If the address is on another network, IP routing using SLIP is implemented. This address is validated via TACACS (when enabled) and the line is put into SLIP mode using the address requested.
Dynamic addressing is useful in a situation where the user needs to know the IP address of a line. A personal computer running an application that automatically dials in using SLIP and polls for electronic mail messages would use dynamic addressing. The application can be set up to dial in periodically and enter the required IP address and password.
Assign a default address to a line with the slip default EXEC command. The transaction is validated by the TACACS server (when enabled) and the line is put into SLIP mode using the address configured with the IP address argument of the slip address dynamic configuration command.
This feature is useful when you do not need to know the IP address to use to gain access to a system, for example, a server that is available to many students on a campus. Instead of requiring each user to know an IP address, they need only enter the EXEC slip default command and let the server select the line to use.
Once a line is configured for SLIP, the EXEC responds to the slip or slip default EXEC commands by turning on SLIP on the line, displaying the Internet address and the size of the largest Internet packet the SLIP support can handle. The line exits SLIP mode when the modem is hung up or an EXEC clear line command is issued. If you are using the auxiliary port (ASM-CS only), you must use the clear line command to exit SLIP mode when the modem is hung up. The auxiliary port does not automatically exit SLIP mode when the modem is hung up.
The no slip line subcommand disables SLIP mode. It has this syntax:
no slipUse this command to disable SLIP on a line that has previously had SLIP enabled.
Your communication server uses the terminal-server or the router implementation of SLIP on a given interface, depending on the address assigned to the SLIP interface.
If the address has a host number of 1, the communication server answer to BootP requests will contain that host's network address, and the host number 2 (instead of 1). This enables dynamic configuration of the remote system's SLIP address. For example, if the host address is 1.0.0.1, the communication server will answer a BootP request by giving the address 1.0.0.2. See the "IP Configuration and Reference" chapter for a description of BootP requests.
To allow SLIP routing on a line, use the following line command:
slip routingThe slip routing configuration command should be used after the line command and before the slip address command, as shown in the following example:
Interface ethernet 0 ip address 128.66.1.1 255.255.255.0 line 6 slip routing slip address dynamic 129.50.3.4 slip header-compression passive
Specify the line you will use for SLIP with the following line subcommand:
line nThe argument n is the number of the line you are configuring for SLIP.
Use either of these slip address line subcommands to assign an interface address, as follows:
slip address address [mask] slip address dynamic [default-address]The argument address is the address of the SLIP interface. The argument mask is the network mask for the associated IP network.
The argument address is the address of the SLIP interface. To specify dynamic addressing, include the optional dynamic keyword. The default-address argument is the address that will be used if a user does not have their own address.
With dynamic addressing, you can use a line for both terminal-server connections and routing connections. When the line is being used for SLIP, the user is prompted for an IP address. If the address the user types in is on the same subnet as the Ethernet, routing will not be implemented. If the address is on a different subnet, routing is implemented.
When a line is configured for dynamic assignment of SLIP addresses, the user enters the slip EXEC command and is prompted for an IP address or logical host name. The address or logical host name is validated via the Terminal Access Controller Access System (TACACS), if TACACS is enabled, and the line is assigned the given address and put into SLIP mode.
The dynamic addressing command is also useful when you need to know the IP address of a line. For example, an application on a personal computer that automatically dials in using SLIP and polls for electronic mail messages can be set up to dial in periodically and enter the required IP address and password.
The following example illustrates a communication server configured to use SLIP. In this configuration one PC is connecting to a network and routing capabilities are not required. Note that the IP address and the SLIP address are on the same subnet, so routing is not implemented.
Interface ethernet 0ip address 1.0.0.1 255.0.0.0line 6slip address dynamic 1.0.0.2
The following user commands illustrate two ways to assign SLIP addresses, using either the default mode or explicitly assigning an address.
To use a default SLIP address, type the following command and the address is automatically assigned.
cs>slip defaultEntering SLIP mode. Your IP address is 1.0.0.2. MTU is 1500 bytes
The following example illustrates the assigning of a specific address with subnet mask.
cs>slip 1.0.0.123 255.255.255.0Password: Entering SLIP mode. Your IP address is 1.0.0.123. MTU is 1500 bytes.
If you are dialing in from a remote router or communication server and you want to route traffic between the SLIP link and local networks, you need full routing capabilities.
The dynamic routing features of the internetwork allow packets to get to their destination and back regardless of the communication server or network they are sent from. For example, if a host such as a laptop computer moves from place to place it can keep the same address no matter where it is dialing in from.
The following example provides an illustration of how a communication server can be configured for routing using CSLIP.
Interface ethernet 0ip address 128.66.1.1 255.255.255.0line 6! default address is terminal-server modelslip routingslip address dynamic 128.66.1.2slip header-compression passive
The slip dedicated line subcommand puts the line in SLIP mode permanently. It has this simple syntax:
slip dedicatedThe communication server will not create an EXEC on the specified line, so it is not available for normal interactive use. No slip EXEC command is necessary to enable SLIP mode.
The following command sequence assigns an Internet address to a SLIP line and permanently puts the line in SLIP mode. Setting the stop bits to 1 enhances performance.
! line 20 location Joe's computer stopbits 1 speed 19200 slip address 182.32.7.51 slip dedicated !
The slip interactive subcommand is generally used to void a slip dedicated line subcommand.
slip interactiveTo put the specified line into SLIP mode, use the EXEC command slip; see "SLIP Connection Types" earlier in this chapter.
Hanging up the modem or clearing the line puts the line back into interactive mode.
The slip hold-queue line subcommand specifies the limit of the SLIP output queue, which stores packets received from the network waiting to be sent to the SLIP client.
slip hold-queue packetsThe argument packets is the maximum number of packets. The default is 3 packets; it is recommended that the queue size does not exceed 10.
This command changes the packet queue length of a line to five packets.
line 2 slip address 182.32.7.5 slip hold-queue 5
Asynchronous lines have relatively low bandwidth and can easily be overloaded, resulting in slow traffic across these lines. One way to make optimal use of available bandwidth is by using Compressed SLIP (CSLIP).
CSLIP uses Van Jacobson TCP header compression (defined by RFC 1144). CSLIP can increase bandwidth availability between two and five times when compared to lines not using header compression. Theoretically, it can improve bandwidth availability by 7:1.
To configure Van Jacobson TCP header compression on the SLIP link, use this line subcommand:
slip header-compression [on|off|passive]Header compression data areas are initialized to handle up to 16 simultaneous TCP connections. Currently, you cannot change this number. You can only turn header compression on or off, or use the passive keyword. The passive keyword prevents the communication server from transmitting compressed packets until it has seen a compressed packet arrive from the SLIP link. If no keyword is specified, passive is the assumed argument.
To force header compression on a line configured for slip header-compression passive, use the EXEC slip command with the optional keyword /compressed.
slip [/compressed] {address|default}The argument address is the IP address to use. The alternative keyword default causes the address specified in the slip address dynamic line configuration subcommand to be used. The slip /compressed command is required to force header compression if both the communication server and the device attached to the communication server are configured for slip header-compression passive.
If a line has been configured for slip header-compression passive, the EXEC slip command with the optional keyword /compressed forces compression to be turned on when the communication server is enters SLIP mode.
cs>slip /compressed defaultcs>slip /compressed 131.108.137.138
Using the /compressed keyword with the slip EXEC command allows the user to force header compression without requiring that the user enter privileged configuration mode.
The /compressed keyword will have no effect on lines not configured for header-compression passive. Lines that are configured for header-compression on will do compression regardless of whether or not the keyword is given and lines that are configured for header-compression off will generate an error message indicating that the line is not configured for header compression.
The following example illustrates the implementation of header compression on the interface with the IP address 128.66.2.1.
cs> slip /compressed 128.66.2.1
Password:
Entering SLIP mode.
Interface IP address is 128.66.2.1, MTU is 1500 bytes.
Header compression is On.
The various items of the asynchronous port configuration are automatically carried over into the asynchronous interface configuration. Specifically, if SLIP header compression is enabled, the interface will also run header compression. You can see this by assigning a SLIP address and observing the text that is displayed in response.
For example, if a line is configured for slip header-compression passive, and you use the slip EXEC command to enter SLIP mode, you will see that the interface is set to match compression status indicated at the EXEC level.
cs>slip 1.0.0.1Password: Entering SLIP mode. Interface IP address is 1.0.0.1, MTU is 1500 bytes Header compression will match your system.
Header compression will match your system indicates that the interface is set to match compression status indicated at the EXEC level. If the line was configured for slip header-compression on, this line would read Header compression is On.
Conserve network resources by configuring communication server asynchronous interfaces as unnumbered. If the asynchronous interface is configured as unnumbered, the interface does not have an address. Network resources are conserved because fewer network numbers are used and routing tables are smaller.
Note that the IP unnumbered feature can be used on the communication server whether or not the system on the other end of the SLIP link knows about this feature. The IP unnumbered feature is transparent to the other end of the link because each system bases its routing activities on information in the routing updates it receives, and on its own interface address on the link.
If the SLIP address is on the local communication server network, the communication server implementation of SLIP is used. If an interface is configured as IP unnumbered and the address is not on the local communication server network, the interface is brought up as unnumbered, and the address entered by the user will be used in BootP responses from the communication server.
Configure an interface to be unnumbered with the following line subcommand:
ip unnumbered interface-nameThe argument interface-name is the name of another interface on which the communication server has an assigned IP address.
The following example provides an illustration of how to configure your communication server for routing using unnumbered interfaces.
Interface ethernet 0ip address 128.66.1.1 255.255.255.0!interface async 6ip unnumbered ether 0!line 6slip routing! default address is terminal-server modelslip address dynamic 128.66.1.2slip header-compression passive
The command below illustrates how the IP unnumbered configuration works. Although the user assigned an address, the system response shows the interface as unnumbered, and the address typed by the user will be used in response to BootP requests.
cs>slip /compressed 1.1.1.1Password: Entering SLIP mode. Interface IP address is unnumbered, MTU is 1500 bytes. Header compression is On.
The slip mtu line subcommand specifies the size of the largest Internet packet that the SLIP support can handle. MTU is the Maximum Transmission Unit.
slip mtu bytesThe argument bytes is the maximum number of bytes. The default is 1500 MTU.
You might want to change to a smaller MTU size if the SLIP application at the other end does not support packets of that size, or you want to assure a lower delay by using shorter packets. This can be desirable when the host Telnet echoing takes longer than 0.2 seconds. For instance, at 9600 baud, a 1500 byte packet takes about 1.5 seconds to transmit, so this delay would indicate that you want an MTU size of about 200.
On the other hand, the MTU size can be negotiated by TCP, regardless of what the terminal settings are, and this is the better way to do it. The communication server performs IP fragmentation of packets larger than the specified MTU. Therefore, do not use this command unless the SLIP implementation supports re-assembly of IP fragments. Since each fragment occupies a spot in the output queue, it may also be necessary to increase the size of the SLIP hold queue.
These commands set the packet MTU size to 200 bytes.
line 5 slip address 182.32.7.5 slip mtu 200
Access lists allow the system administrator to control the hosts that may be accessed by a PC running SLIP through a communication server. Separate access lists can be defined for SLIP and for normal connections. The software allows separate access lists to be defined for use when the line is running SLIP.
To configure an access list to be used on packets from the SLIP host, use this line subcommand:
slip access-class number inWhen this command is entered, the IP destination address of each packet is run through the access list for acceptability, and dropped or passed. The argument number is the IP access list number (see the section "Configuring IP Access Lists" in the "IP Configuration and Management" chapter for information about IP access lists).
To specify an access list to be used on packets being sent to the SLIP host, use this line subcommand:
slip access-class number outWhen this command is entered, the IP source address is compared against the access list, and only those packets allowed by the access list are transmitted on the asynchronous line. The argument number is the IP access list number (see the section "Configuring IP Access Lists" in the the"IP Configuration and Management" chapter for information about IP access lists).
This example assumes that SLIP users are restricted to certain servers designated as SLIP servers, but that normal terminal users can access anything on the local network.
! access list for normal connections access-list 1 permit 131.108.0.0 0.0.255.255 ! ! access list for SLIP packets. access-list 2 permit 131.108.42.55 access-list 2 permit 131.108.111.1 access-list 2 permit 131.108.55.99 ! !Define all the lines with slip addresses and !appropriate access lists line 1 60 slip address dynamic access-class 1 out slip access-class 2 in !
The BootP (Boot Protocol) server for SLIP supports the extended BootP requests specified in RFC 1084. These requests are specified with the async-bootp global configuration command. The full syntax for this command follows:
async-bootp tag [:hostname] data...The argument tag is the item being requested, and is one of the following expressed as file name, integer, or IP dotted decimal address:
Use the optional argument :hostname to indicate that this entry applies only to the host specified. The argument :hostname accepts both an IP address and logical host name.
The argument data can be a list of IP addresses entered in dotted decimal notation or as logical host names, a number, or a quoted string.
If no extended BootP commands are entered, by default the software generates a gateway and subnet mask appropriate for the local network.
Use the EXEC command show async-bootp to list the configured parameters. Use the no async-bootp command to clear the list.
The following example illustrates how to specify different boot files, one for a PC, and one for a Macintosh. With this configuration, a BootP request from the host on 128.128.1.1 results in a reply listing the boot file name as pcboot. A bootP request from the host named mac results in a reply listing the boot file name as macboot.
async-bootp bootfile :128.128.1.1 "pcboot" async-bootp bootfile :mac "macboot"
The following example specifies a subnet mask of 255.255.0.0.
async-bootp subnet-mask 255.255.0.0
The following example specifies a negative time offset of the local subnetwork of -3600 seconds.
async-bootp time-offset -3600
The following example specifies the IP address of a time server.
async-bootp time-server 128.128.1.1
The Point-to-Point Protocol (PPP) is a method of encapsulating Internet Protocol (IP) datagrams and other Network Layer protocol information over point-to-point links. The document "Point-to-Point Initial Configuration Options" defines the set of options that are negotiated during startup.
Of the possible upper-layer protocols, only IP is supported at this time. Thus, the only upper-level protocol that can be sent or received over a point-to-point link using PPP encapsulation is IP.
The Point-to-Point Protocol is enabled on an interface using the encapsulation interface subcommand followed by the ppp keyword. Synchronous and asynchronous lines can be configured for PPP encapsulation.
To configure PPP encapsulation on an asynchronous serial interface, use the slip line subcommands to configure the line as desired, then use the encapsulation interface subcommand to set the encapsulation to PPP.
The command to implement PPP encapsulation is as follows:
encapsulation pppThese commands enable PPP encapsulation on synchronous serial interface zero.
interface serial 0 encapsulation ppp
These commands enable PPP encapsulation on an asynchronous serial interface.
interface async 3 encapsulation ppp
The following example shows a line being configured for PPP encapsulation on an asynchronous serial interface. First, the slip line subcommands is used to configure the line as desired, then the encapsulation interface subcommand is used to set the encapsulation to PPP as shown below:
line 5 slip routing slip address dynamic interface async 5 encapsulation ppp
This section contains five examples of SLIP routing configurations. Each configuration is designed to meet different communication requirements.
Possible communication server configurations range from simple to complex. The following example illustrates a simple configuration that allows routing and dynamic addressing. In this configuration the communication server will act as either a communication server or a router, depending on the user-specified address.
The following example illustrates a simple configuration that allows routing and dynamic addressing. In this configuration the communication server will act as either a terminal server or a router, depending on the user-specified address.
! allow all lines to run SLIP with user-specified address on or off our local ! network.line 1 16slip routingslip address dynamic
The following example illustrates a more complex configuration that allows IP routing using TCP header compression, and limits the traffic across the low-bandwidth asynchronous SLIP lines.
interface async 7ip address 150.136.79.0 255.255.255.0! apply access listaccess-group 1! Do accountingip accounting! forward broadcasts.ip helper address 131.108.1.255!! run "Van Jacobson" TCP header compression on demandip tcp header-compression passive!! use priority queuing for small interactive packets (for example, telnet)! run RIP routing so that PCs and SUNs, and other workstations can send! dynamic routing info without having to know about IGRProuter ripnetwork 150.136.0.0! Do not use RIP on the ethernetpassive-interface ether 0router igrp 109network 150.136.0.0! do not send big routing updates down the link. Each remote host! must use the SLIP link as the default route.passive-interface async 7! redistribute the routing information received from RIPredistribute rip
In this configuration, the communication server is set up as a dedicated dial-in router. No terminal-server model SLIP connections are allowed. The interfaces are all configured as IP unnumbered.
ip routinginterface ether 0ip address 1.0.1.1 255.255.255.0!interface async 1ip unnumbered ether 0interface async 2ip unnumbered ether 0interface async 3ip unnumbered ether 0interface async 4ip unnumbered ether 0interface async 5ip unnumbered ether 0!line 1slip routing! the slip addresses are not used except to reply to BootP requests. Normally,! the routers dialing in will have their own address, and not use BootP at all.slip address 1.0.2.1line 2slip routingslip address 1.0.3.1line 3slip routingslip address 1.0.4.1line 4slip routingslip address 1.0.5.1line 5slip routingslip address 1.0.6.1!line 1 5slip header-compression passiveslip dedicated!! run RIP on the asynchronous lines, because few implementations of SLIP ! understand IGRP. Run IGRP on the ethernet (and in the local network).!router igrp 109network 1.0.0.0! send routes from the asynchronous lines on the production network.redistribute RIP! don't send IGRP updates on the async interfacespassive-interface async 1passive-interface async 2passive-interface async 3passive-interface async 4passive-interface async 5!router RIPnetwork 1.0.0.0redistribute igrppassive-interface ethernet 0! consider filtering everything except a default route from the routing! updates sent on the (slow) asynchronous linesdistribute-list 1 out!
In this example, one of the SLIP lines is used as the only network interface. The communication server is used primarily as a terminal server, but is at a remote location and dials into the central site for its only network connection.
interface ethernet 0shutdown! notice that the asynchronous interface is not explicitly configured;! rather, it is created dynamically when the SLIP configuration! is entered.line 1slip routingslip header-compression onslip address 1.0.0.1slip dedicatedip default-gateway 1.0.0.2!
A communication server can be configured to support all server functions. A user can dial in and use the port for Telnet connections, LAT connections, TN3270, XRemote, SLIP to a single PC, or SLIP routing. Note that in this example, only IGRP routing is running; it is assumed that the systems that are dialing in to use routing will either support IGRP or have some other method (for example, a static default route) of determining that the communication server is the best place to send most of its packets.
interface ether 0ip address 1.0.0.1 255.255.255.0!router igrp 109network 1.0.0.0!line 1 5slip routingslip header-compression passivemodem ri-is-cd!line 1slip address dynamic 1.0.0.101line 2slip address dynamic 1.0.0.102line 3slip address dynamic 1.0.0.103line 4slip address dynamic 1.0.0.104line 5slip address dynamic 1.0.0.105!
This section describes the EXEC command for maintaining SLIP support on the communication server.
Maintaining SLIP is a simple task on the communication server. The clear line EXEC command disables SLIP mode and starts an EXEC process on a nondedicated SLIP line. Enter this command at the EXEC prompt:
clear line line-numberThe argument line-number specifies the line. This command is the only way to exit SLIP mode on a line without modem control.
Use the EXEC show commands described in this section to obtain displays of activity on the SLIP line.
The show ip aliases command displays Internet addresses mapped to TCP ports (aliases) and SLIP addresses, which are treated similarly to the aliases. Enter this command at the EXEC prompt:
show ip aliasesTo distinguish a SLIP address from a normal alias address, the command output uses the form SLIP TTYn for the port number, where n is the terminal number (in octal).
Sample output follows:
cs> show ip aliases
IP Address Port
192.31.7.52 SLIP TTY35
192.31.7.53 SLIP TTY36
192.31.7.54 SLIP TTY37
192.31.7.55 SLIP TTY40
The display lists the IP address and corresponding port number.
The show ip arp EXEC command displays the Address Resolution Protocol (ARP) cache, where SLIP addresses appear as permanent ARP table entries. To display the IP ARP cache, use the following EXEC command:
show ip arpAn Address Resolution Protocol establishes correspondences between network addresses (an IP address, for example) and LAN hardware addresses (Ethernet addresses). A record of each correspondence is kept in a cache for a predetermined amount of time and then discarded. Following is sample output. Table 1-1 describes the fields displayed.
cs> show ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 131.108.1.140 137 aa00.0400.6408 ARPA Ethernet0
Internet 131.108.1.111 156 0800.2007.8866 ARPA Ethernet0
Internet 131.108.1.115 33 0000.0c01.0509 ARPA Ethernet0
Internet 192.31.7.24 5 0800.0900.46fa ARPA Ethernet2
Internet 192.31.7.26 41 aa00.0400.6508 ARPA Ethernet2
Internet 192.31.7.27 - aa00.0400.0134 ARPA Ethernet2
Internet 192.31.7.28 67 0000.0c00.2c83 ARPA Ethernet2
Internet 192.31.7.17 67 2424.c01f.0711 ARPA Ethernet2
Internet 192.31.7.18 64 0000.0c00.6fbf ARPA Ethernet2
Internet 192.31.7.21 114 2424.c01f.0715 ARPA Ethernet2
Internet 131.108.1.33 15 0800.2008.c52e ARPA Ethernet0
Internet 131.108.1.55 44 0800.200a.bbfe ARPA Ethernet0
Internet 131.108.1.6 89 aa00.0400.6508 ARPA Ethernet0
Internet 131.108.7.1 - 0000.0c00.750f ARPA Ethernet3
Internet 131.108.1.1 - aa00.0400.0134 ARPA Ethernet0
| Field | Description |
|---|---|
| Protocol | Protocol for network address in Address field |
| Address | The network address that corresponds to Hardware Addr |
| Age (min) | Age, in minutes, of the last update of the cache entry |
| Hardware Addr | LAN hardware address that corresponds to network address |
| Type | Type of ARP (Address Resolution Protocol):
ARPA = Ethernet-type ARP SNAP = RFC1042 ARP Probe = HP Probe Protocol |
| Interface | Interface that has the corresponding Address |
The show line EXEC command displays SLIP status for a line running in SLIP mode. Enter this command at the EXEC prompt:
show line line-numberThe argument line-number specifies the line.
Following is sample output of this command.
tarmac> show line 1
Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns
1 TTY 9600/9600 - - - - - 0 1 0
Line 1, Location: "", Type: ""
Length: 24 lines, Width: 80 columns
Baud rate (TX/RX) is 9600/9600, no parity, 2 stopbits, 8 databits
Status: Ready
Capabilities: SLIP allowed
Modem state: Ready noCTS noRING
Special Chars: Escape Hold Stop Start Disconnect Activation
^^x none - - none
Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch
0:10:00 never 0:00:15 not imp not set
Session limit is not set.
Allowed transports are telnet lat pad rlogin. Preferred is lat
No output characters are padded
Characters causing immediate data dispatching:
Char ASCII
SLIP header compression enabled
Group codes: 0
Following is sample output of the show line command without the line-number argument.
cs> show line 1
Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise
0 CTY - - - - - 1 0
1 SLIP 9600/9600 - - - - - 0 0
2 TTY 9600/9600 - - 1 - - 0 0
3 TTY 9600/9600 - inout 1 - - 0 0
4 TTY 9600/9600 - - - - - 0 0
* 5 TTY 9600/9600 - - - - - 1 0
6 SLIP 9600/9600 - - - - - 0 0
7 TTY 9600/9600 - - - - - 0 0
10 TTY 9600/9600 - - - - - 0 0
11 TTY 9600/9600 - - - - - 0 0
12 TTY 9600/9600 - inout - - - 0 0
13 TTY 9600/9600 - - - - - 0 0
14 TTY 9600/9600 - - - - - 0 0
15 TTY 9600/9600 - - - - - 0 0
16 TTY 9600/9600 - - - - - 0 0
17 TTY 9600/9600 - - - - - 0 0
| Field | Description |
|---|---|
| Tty | Line number in octal or decimal (depending on the setting of the service decimal-tty global configuration command) |
| * | Active line |
| Type | The line type |
| Tx/Rx | Current transmit and receive baud rates |
| Modem | Handling, if any, of RS-232 modem control signals |
| Roty | Rotary group number |
| Acc0 | Access class for outgoing connections |
| Acc1 | Access class for incoming connections |
| Uses | Total number of connections made to or from the terminal line since the system was booted |
| Noise | Total number of characters received ("noise" characters) as a framing error or when the line is inactive |
The show slip EXEC command displays the status of all lines configured for SLIP support. Enter this command at the EXEC prompt:
show slipFollowing is sample output. Table 1-3 describes the fields displayed by this command.
cs>show slipSlip statistics: Rcvd: 82514 packets, 0 bytes, 21478 escapes 414 format errors, 2 checksum errors, 0 overrun, 0 no buffer Sent: 70656 packets, 0 bytes, 161701 escapes, 1135 dropped Tty Mod Address Istate Ostate Qd InPack OutPac Inerr Dropped MTU Qsz 1 i/o 131.108.1.230 IDLE IDLE 0 0 0 0 0 1524 3 2 i/o 131.108.1.231 IDLE IDLE 0 3 0 0 0 1524 3 3 i/o 131.108.1.232 IDLE IDLE 0 4375 3994 0 9 1524 3 4 i/o 131.108.1.233 IDLE IDLE 0 24 22 0 0 1524 3 5 i/o 131.108.1.245 IDLE IDLE 0 955 1035 0 1 1524 3 6 i/o 131.108.1.246 IDLE IDLE 0 0 0 0 0 1524 3 7 i/o 131.108.1.247 IDLE IDLE 0 15 8 0 0 1524 3 10 i/o 131.108.1.248 IDLE IDLE 0 3167 2599 0 54 1524 3 * 11 i/o 131.108.1.249 RECV IDLE 0 1753 1475 0 30 1524 3 12 i/o 131.108.1.250 IDLE IDLE 0 0 0 0 0 1524 3 13 i/o 131.108.1.251 IDLE IDLE 0 0 0 0 0 1524 3 14 i/o 131.108.1.252 IDLE IDLE 0 30761 25854 0 423 1524 3 15 i/o 131.108.1.234 IDLE IDLE 0 4900 5734 0 166 1524 3 16 i/o 131.108.1.235 IDLE IDLE 0 0 0 0 0 1524 3 16 i/o 131.108.1.235 IDLE IDLE 0 0 0 0 0 1524 3 17 i/o 131.108.1.236 IDLE IDLE 0 3393 3256 0 31 1524 3 20 i/o 131.108.1.237 IDLE IDLE 0 4 0 0 0 1524 3
| Field | Description |
|---|---|
| Rcvd: | Statistics on packets received |
| packets | Packets received |
| bytes | Total number of bytes |
| escapes | Count of escape characters received |
| format errors | Packets with a bad IP header, even before the checksum is calculated |
| checksum errors | Count of checksum errors |
| overrun | Number of giants received |
| no buffer | Number of packets received when no buffer was available |
| Sent | Statistics on packets sent |
| packets | Packets sent |
| bytes | Total number of byte |
| escapes | Count of escape characters sent |
| dropped | Number of packets dropped |
| Tty mod | Type of modem control |
| Address | IP address of the line |
| IState and OState | Used by technical support for troubleshooting |
| Qd | Number of packets on hold queue (Qsz is max) |
| InPack | Number of packets input for asynchronous line |
| OutPac | Number of packets sent to asynchronous line |
| Inerr | Number of total input errors; sum of format errors, checksum errors, overruns and no buffers |
| Dropped | Number of packets received that would not fit on the hold queue (time to either fix the hosts' TCPs, or increase the hold queue size) |
| MTU | The maximum packet size, in bytes, that the interface will
handle |
| Qsz | The maximum number of packets allowed to be in the queue before packets are dropped (in order to maintain congestion control) |
| * | An asterisk indicates a line currently in SLIP mode |
The show async-bootp EXEC command displays the parameters that have been configured for SLIP extended BootP requests. Enter this command at the EXEC prompt:
show async-bootpFollowing is sample output:
cs> show async-bootp
The following extended data will be sent in BOOTP responses:
bootfile (for address 128.128.1.1) "pcboot"
bootfile (for address 131.108.1.111) "dirtboot"
subnet-mask 255.255.0.0
time-offset -3600
time-server 128.128.1.1
The privileged-mode EXEC debug commands described in this section are used to troubleshoot lines in SLIP mode. Generally, you enter these commands during troubleshooting sessions with Cisco staff.
For each debug command, there is a corresponding undebug command that turns the display off. Entering the debug commands will affect performance of the SLIP feature.
The debug slip EXEC command enables logging of all SLIP activity. The high volume of SLIP debugging output, which amounts to several lines per packet, noticeably affects overall system performance.
The debug slip-event EXEC command enables logging of selected SLIP events, such as various types of errors, enabling and disabling of SLIP mode on a line, and so on. The volume of output for this command is much lower than that for the debug slip command.
This section provides an alphabetically arranged summary of the SLIP global configuration commands.
[no] async-bootp tag [:hostname] data...
Specifies extended BootP requests as defined in RFC1084. The argument tag is the item being requested, and is one of the following:
The optional argument :hostname indicates that this entry applies only to the host specified. The argument :hostname accepts both an IP address and logical host name. The argument data can be a list of IP addresses entered in dotted decimal notation or as logical host names, a number, or a quoted string. Use the no async-bootp command to clear the list.
Following is a list of alphabetically arranged SLIP interface commands. Refer to the section "Configuring Asynchronous Lines" in the "System Configuration" chapter for additional information about line configuration.
Configures an interface to be unnumbered. The argument interface-name is the name of another interface on which the communication server has an assigned IP address.
Specifies the line you will be using for SLIP. The argument n is the number of the line you are configuring for SLIP.
Following is a list of alphabetically arranged SLIP line configuration subcommands. Refer to the section "Configuring Asynchronous Lines" in the "System Configuration" chapter for additional information about line configuration.
Cancels SLIP support on the line.
slip access-class number {in|out}
Configures an access list to be used on packets to or from the SLIP host. The argument number is the IP access list number. The keyword in configures a list for packets from the SLIP host; keyword out compares the IP source address against the access list, and only those packets allowed by the access list are transmitted on the asynchronous line.
Assigns an interface address. The argument address is the address of the of the SLIP interface. The argument mask is the network mask for the associated IP network.
slip address dynamic [default-address]
Assign an interface address. The argument address is the address of the SLIP interface. To specify dynamic addressing, include the optional dynamic keyword. The default-address argument is the address that will be used if a user does not have their own address.
Places the line in SLIP mode permanently. The communication server will not create an EXEC on this line, so it is not available for normal interactive use.
slip header-compression {on|off|passive}
Configures Van Jacobson TCP header compression on the SLIP link. Header compression data areas are initialized to handle up to 16 simultaneous TCP connections. Currently, you cannot change this number. You can only turn header compression on or off, or use the passive keyword. The passive argument will prevent the communication server from transmitting compressed packets until it has seen a compressed packet arrive from the SLIP link. If no keyword is specified, passive is the assumed argument.
Specifies the limit of the SLIP output queue, which stores packets received from the network waiting to be sent to the SLIP client. The argument packets is the maximum number of packets. Default is two packets.
Allows the line to be used in either SLIP mode or interactive mode. Hanging up the modem or clearing the line puts the line back into interactive mode.
Specifies the size of the largest Internet packet that the SLIP support can handle. The argument bytes is the maximum number of bytes. Default is 1500 bytes.
slip routing
Enables SLIP routing on a line.
This section lists and summarizes SLIP and CSLIP user commands discussed in this chapter.
slip [/compressed] {address|default}
Forces header compression to be activated on a line configured for slip header-
compression passive. The argument address is the IP address of the interface on which you want to implement header compression. Using the alternative keyword default, the line is put into SLIP mode using the address in the IP address argument of the slip address dynamic configuration command.
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