Jan 10 2009
IRDP an alternative to HSRP, VRRP or GLBP
IRDP is an alternative technology to HSRP, VRRP, GLBP and the like.
IRDP makes use of ICMP messages to inform hosts of a default gateway they can use.
Consider the toplogy below.
R2 and R3 announce themselves as default gateways to R1. R2 is configured with an IRDP preference of 10 and R3 is configured with an IRDP preference of 20. R1 chooses the lowest preference as the default gateway ie R2, however the Cisco implementation of this seem to conflict with the RFC(RFC 1256) which states:-
A Router Advertisement includes a “preference level” for each advertised router address. When a host must choose a default router address it is expected to choose from those router addresses that have the highest preference level.
Watch the video below or click here to download and watch it on your iPod.
The commands used in the irdp configuration can be found below.
R1
!
no ip routing
!
ip gdp irdp
!
interface FastEthernet1/0
ip address 10.0.0.1 255.255.255.0
R2
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface FastEthernet1/0
ip address 10.0.0.2 255.255.255.0
ip irdp
ip irdp preference 10
R3
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface FastEthernet1/0
ip address 10.0.0.3 255.255.255.0
ip irdp
ip irdp preference 20