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frame-relay PVC x 2 same IP address why

If we have 2 frame-relay PVC configurd with the same IP address and both are up which one will traffic get routed over by default say I pinged from one end to the other? why would one do this same IP on different DLCI as apposed to assigning different ones. The reason I ask is I have come across this scenario at clients site and Im trying to work out why this was configured this way

interface Serial0/3/0

no ip address

encapsulation frame-relay

no keepalive

no fair-queue


interface Serial0/3/0.1 point-to-point

ip address

frame-relay interface-dlci 101


interface Serial0/3/0.2 point-to-point

ip address

frame-relay interface-dlci 102


Re: frame-relay PVC x 2 same IP address why

That's something I'd like to hear to.

I think it will probably load balance between the 2 interfaces.

But I've tested it.

And the router put both interfaces on the routing table:

r1# sh ip route | b Gatew

Gateway of last resort is not set

C is directly connected, Serial1/0.1

is directly connected, Serial1/0.2

But it seems to send packets only using 1 interface:

Pinging from the other router:


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 44/91/156 ms


*Mar 1 00:08:13.963: IP: tableid=0, s= (local), d= (Serial1/0.2), routed via FIB

*Mar 1 00:08:13.967: IP: s= (local), d= (Serial1/0.2), len 100, sending

*Mar 1 00:08:13.967: ICMP type=8, code=0

*Mar 1 00:08:14.115: IP: s= (Serial1/0.1), d=, len 100, rcvd 2

*Mar 1 00:08:14.115: ICMP type=0, code=0

*Mar 1 00:08:14.119: ICMP: echo reply rcvd, src, dst


Cisco Employee

Re: frame-relay PVC x 2 same IP address why

This is certainly allowed by IOS on serial interfaces but could definitely cause issues, especially if a routing protocol such as ospf is used.

If the goal was to save IP address space then I would recommend looking at "ip unnumbered" interfaces.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
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