From: Gupta, Gopal (NWCC) (gopal.gupta@hp.com)
Date: Tue Apr 15 2008 - 13:24:39 ART
Hi Luca,
It is surely possible to have two different encapsulations between 2 ends of the routers and still they can talk because of the Rotuers' behavior that they support both of the Encapsulations and when they see the packet coming with different encapsulation they understand that packet and process according to the incoming encapsulation.
Cisco went a mile further and as such Cisco routers understands both 'IETF' and 'CISCO' encapsulations. When this near-end router uses 'CISCO' encapsulation, it merely means that at layer 2, it is going to encapsulate all out going packets with "CISCO encapsulating Language engine" incoming packets can be decapsulated even if they are coming as 'CISCO' or 'IETF' . The same logic applies when the far end router have 'IETF' as its 'encapsulating language'
http://cciepursuit.wordpress.com/2007/09/14/frame-relay-encapsulation-mismatches/
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Luca Hall
Sent: Tuesday, April 15, 2008 19:53
To: ccielab@groupstudy.com
Subject: FR Encap
Importance: Low
r4 and r5 connected to the frame-relay switch:
r4(s0/0) -- fr-sw -- (s0/0)r5
r4 uses fr encapsulation of cisco:
r4#sh int s0/0 | in Encap
Encapsulation FRAME-RELAY, loopback not set
r4#sh run int s0/0
interface Serial0/0
ip address 45.1.1.4 255.255.255.0
encapsulation frame-relay
no ip route-cache cef
no ip route-cache
ip ospf network non-broadcast
ip ospf priority 0
frame-relay map ip 45.1.1.5 405
no frame-relay inverse-arp
end
r4#sh ip int brie | i up
Serial0/0 45.1.1.4 YES manual up up
r5 uses frame-relay encapsulation of ietf:
r5#sh int s0/0 | in Encap
Encapsulation FRAME-RELAY IETF, loopback not set
r5#sh run int s0/0
interface Serial0/0
ip address 45.1.1.5 255.255.255.0
encapsulation frame-relay IETF
no ip route-cache cef
no ip route-cache
ip ospf network non-broadcast
frame-relay map ip 45.1.1.4 504 IETF
no frame-relay inverse-arp
end
r5#sh ip int brief | in up
Serial0/0 45.1.1.5 YES manual up up
From everything I have ever read these two shouldn't be able to talk
as encapsulation must match between cpe's, but they can:
r4#ping 45.1.1.5
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 45.1.1.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/60/64 ms
I have shut the interfaces in every way I can think of and then saved and
reloaded them both and I still have the same result. I cant figure out why
they can still talk.
Also anyone know a command similar to `debug ip packet dump` for frame
so you could put the frame into a analyzer?
Thanks
Pass the CCIE in six weeks, Guaranteed!
http://www.certscience.com/CCIE
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