Help with HSRP

Unanswered Question
Sep 26th, 2009
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Hi Guys,


I am deploying two 3750E's in my netwrok. One of the 3750E switch at site A will have two eBGP networks. The 3750E on the second site willl have 1 eBGP peering. All the 3 eBGP peerings are with the same company only. So, on all the three links I will have the same network prefixes coming in. The two 3750E's are connected with each other and will be runnintg iBGP between the.


What I want is that if link1 goes down at site A then the traffic shoul go through the link 2 in Site A. Only when both the links in site A are down then only the traffic should be routed to site B. I can achieve this using weights in BGP. My main problem is hopw do I configure HSRP between the Site A and Site B.


--> If I use route tracking for the remote subnet then HSRP won't work because of the iBGP between Site A and Site B. So even if both the links go down at Site A the subnet will be still available via the iBGP connection. HSRP won't fail over.

--> If I use interface tracking then which interface should I track. If I track the WAN interface the when link 1 goes down then HSRP kicks in and starts sending the traffic towards SIte B even though Link 2 is up.


Site A

Link 1 and Link 2

Site B

Link 3


Traffic to moce out on Link 1 if it fails then Link 2 and if both LInk 1 and Link 2 fails then only Link 3 should come into the picture.




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Giuseppe Larosa Sat, 09/26/2009 - 03:49
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Hello Sauray,

you need to use interface tracking but you need to increase priority of Site A so that if one link fails site A is still the HSRP master.


int vlan 100

ip address 10.10.100.2 255.255.255.0

standby 100 ip 10.10.100.1

standby 100 priority 115

standby 100 preempt

standby 100 track interface wan1

standby 100 track interface wan2



SW2


int vlan 100

ip address 10.10.100.3 255.255.255.0

standby 100 ip 10.10.100.1

standby 100 priority 100

standby 100 preempt

standby 100 track interface wan3




each tracked interface when fails decrements of 10 the priority.

With this config if either wan1 or wan2 fails priority becomes 115-10 = 105


Hope to help

Giuseppe



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