Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

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 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

2 REPLIES

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 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

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)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
112
Views
0
Helpful
2
Replies