frame-relay PVC x 2 same IP address why

[allan.wells]

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 192.1.1.1 255.255.255.0

frame-relay interface-dlci 101

!

interface Serial0/3/0.2 point-to-point

ip address 192.1.1.1 255.255.255.0

frame-relay interface-dlci 102

[vladrac-ccna]

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 192.1.1.0/24 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:

r2#p 192.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.1.1.1, timeout is 2 seconds:

!!!!!

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

r2#

*Mar 1 00:08:13.963: IP: tableid=0, s=192.1.1.2 (local), d=192.1.1.1 (Serial1/0.2), routed via FIB

*Mar 1 00:08:13.967: IP: s=192.1.1.2 (local), d=192.1.1.1 (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=192.1.1.1 (Serial1/0.1), d=192.1.1.2, 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 192.1.1.1, dst 192.1.1.2

Vlad

[Harold Ritter]

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,