From: richard.harvey@nbs.nhs.uk
Date: Wed Aug 24 2005 - 06:18:16 GMT-3
I'm having an interesting problem with CEF and peer(ppp) neighbor-route:
CAT1--------R3(s0/1.1)----------R4---------rest of network
hostname R3
!
ip cef
!
interface Serial0/1
no ip address
encapsulation frame-relay
no frame-relay inverse-arp
!
interface Serial0/1.1 point-to-point
frame-relay interface-dlci 503 ppp Virtual-Template1
!
interface Virtual-Template1
ip address 172.16.34.3 255.255.255.0
no peer neighbor-route
ppp authentication chap
!
You can not ping 'through' R3 from CAT1 when traffic has to exit the PPP link. If you add 'peer neighbor-route' or disable CEF then all is good again. Looking at 'show ip cef' you see that with no peer route configured, you do not have a /32 adjacency for the router at the remote-end of the PPP link (R4). All you have is the /24 entry, which as I understand it is not enough for CEF to correctly forward the packet.
Adding the neighbor route back in and reseting the interface brings the correct entry into CEF.
R3#sh ip cef | i /32
0.0.0.0/32 receive
172.16.34.0/32 receive
172.16.34.3/32 receive << Entry for local side, but none for remote
172.16.34.255/32 receive
172.16.38.0/32 receive
172.16.38.3/32 receive
172.16.38.10/32 172.16.38.10 FastEthernet0/0
172.16.38.255/32 receive
172.16.103.0/32 receive
172.16.103.1/32 receive
172.16.103.255/32 receive
255.255.255.255/32 receive
Is this a known limitation of CEF with PPP neighbor routes or am I mis-understanding how CEF works?
Richard Harvey
Networks & Security Engineer
National Blood Service
Desk: 020 8271 6509
Mob: 0776 428 0945
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