Question about IRDP

From: George Zhang (gyzhang63@xxxxxxxxxxx)
Date: Fri Mar 01 2002 - 14:12:49 GMT-3


   
I have a question about IRDP preference. Consider the following scenario:

           R3-E0-------------------E0-R4
                         |
                         |
                        E0
                        R1

R3's config:
  in e0
    ip ad 172.16.1.3 255.255.255.0
    ip irdp
    ip irdp preference 300

R4's config:
  in e0
    ip ad 172.16.1.4 255.255.255.0
    ip irdp
    ip irdp preference 400

R1's config:

  no ip routing
  in e0
    ip ad 172.16.1.1 255.255.255.0

IRDP is configured on R3 and R4's ethernet 0. IP routing is turned off on
R1. So it is acting as a host.

Question: Which router is the default gateway for R1? R3 or R4?

According to the Doc CD:

preference number
(Optional) Preference value. The allowed range is -231 to 231. The default
is 0. A higher value increases the router's preference level. You can modify
a particular router so that it will be the preferred router to which others
home.

My understanding is that the router with a higher preference valve, i.e. R4
will win.

However, the following route table on R1 shows the opposite:

r1#sh ip route
Gateway Using Interval Priority Interface
172.55.255.3 IRDP 788 300 Ethernet0/1
172.55.255.4 IRDP 900 400 Ethernet0/1
Default gateway is 172.55.255.3
Host Gateway Last Use Total Uses Interface
ICMP redirect cache is empty

Could someone please explain this?

Thanks.

George Zhang



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