From: Andrew Bruce Caslow (abcaslow@netmasterclass.net)
Date: Tue May 31 2005 - 09:21:57 GMT-3
Hi Kim,
Related to this matter, a question I have for you is: how far have you
proceeded in your configuration. Have you enabled a routing protocol over
the link? If not, please remember this: A ping will not work until routing
is configured. If a routing protocol has not been enabled, there is no
subnet entry in "sh ip route" at the moment. For example, if you enables RIP
on both sides, then ping will work.
Another work around for this situation is to enable PPP encapsulation and
use the "peer neighbor-route" feature. As an example, examine the
configurations below. It is a slight variation to your question, but once
you understand this configuration, I think it will be easier for you to
understand the "ip unnumbered" configuration.
In the configurations below, routers R3 and R5 are directly connected via a
back to back serial link. Notice how the addresses on both ends of this
common link use a different address. R3 is assigned 3.3.3.3 and R5 is
assigned 5.5.5.5. However, they can ping each other because of the PPP "peer
neighbor-route" feature. Notice how the remote IP address of the other end
of the link is in each router's forwarding table as a /32. For example, the
5.5.5.5/32 route is in the forwarding table of R3.
Router R3
r3(config-if)#do sh run inte s0/1
!
interface Serial0/1
ip address 3.3.3.3 255.255.255.0
encapsulation ppp
end
r3(config-if)#do s ip ro | b Gate
Gateway of last resort is not set
3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Serial0/1
5.0.0.0/32 is subnetted, 1 subnets
C 5.5.5.5 is directly connected, Serial0/1
Router R5
r5(config-if)#do sh run inte s1/1
!
interface Serial1/1
ip address 5.5.5.5 255.255.255.0
encapsulation ppp
clockrate 56000
end
r5(config-if)#do sh ip ro | b Gate
Gateway of last resort is not set
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Serial1/1
5.0.0.0/24 is subnetted, 1 subnets
C 5.5.5.0 is directly connected, Serial1/1
Once you understand this, perform these following three steps:
1). remove these IP addresses from the Serial interfaces, assign
2). Assign these addresses to a loopback interface (as an example, Loopback
0)
3). Enter the following command on each Serial interface connecting R3 and
R5: "ip unnumbered lo0"
You will see the remote address appear in the local forwarding tables as a
/32 entry and you will be able to ping the addresses.
HTH,
-Bruce
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of B Kim
Sent: Sunday, May 29, 2005 5:15 PM
To: CCIE Study Group
Subject: Need help for NMC Workbook 8.1
R3 s0/1 is connected via serial to R5 s1/1. Requirement is that create
Frame Relay point-to-point subinterfaces over the serial link without
Frame Relay switching. Do not create any IP subnet over the link.
The workbook solution: Disable LMI by no keepalive command, and use ip
unnumbered. Configure Frame Relay point-to-point subinterface with the
same DLCI on both sides. Ping should work.
I could understand the solution so far. My problem is the pinging: Ping
each other's loopback address doesn't seem to work.
Could anyone explain why R3 and R5 can or cannot ping each other's
loopback address?
Thanks in advance.
R3:
!
interface Loopback0
ip address 172.16.103.1 255.255.255.0
!
!
interface Serial0/1
no ip address
encapsulation frame-relay
no keepalive
no frame-relay inverse-arp
!
interface Serial0/1.1 point-to-point
ip unnumbered Loopback0
frame-relay interface-dlci 503
!
R5:
!
interface Loopback0
ip address 172.16.105.1 255.255.255.0
!
!
interface Serial1/1
no ip address
encapsulation frame-relay
no keepalive
clockrate 128000
no frame-relay inverse-arp
!
interface Serial1/1.1 point-to-point
ip unnumbered Loopback0
frame-relay interface-dlci 503
!
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