failover at L3 switch level

[ravi mishra]

still doubtful..i have 2 ISP links.And want to implement the 2nd link as a failover link to the first at the L3 switch level.how can i do it?..is it possible?..if it is then what protocol is required to do so.please help

[paul driver · Accepted solution]

Hello

You dont really require any routing protocols to do this, you can use "floating" static routing with ip sla tracking to accommodate this.

This means you have two defaults routes pointing to either ISP next hop address and then you give preference to which route path traffic should take. ( the lower the number the highest preference the path) add ip sla and tracking and you have a nice resilient setup.

ip sla 5

icmp-echo (isp1-nexthop) source-ip x.x.x.
ip sla schedule 5 life forever start-time now

track 10 ip sla 5 reachability

ip route 0.0.0.0 0.0.0.0 isp1 track 10 1

ip route 0.0.0.0 0.0.0.0 isp2  2

res

Paul

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Thanks.

[jawad-mukhtar · Accepted solution]

create two track

track1 (for isp1)

track2 (for isp2)

ip sla 1

icmp-echo (isp1 GW) source-ip x.x.x.
ip sla schedule 1 life forever start-time now

ip sla 2

icmp-echo (isp2 GW) source-ip x.x.x.
ip sla schedule 2 life forever start-time now

ip route 0.0.0.0 0.0.0.0 ISP1 (next hope IP of device on which ISP1 is terminated) track 1

ip route 0.0.0.0 0.0.0.0 ISP2 (next hope IP on device which ISP2 is terminated) track 2

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Jawad

[paul driver]

@Jawad

Why would you need to track both ISP interfaces?

ISP1 is the primary and this is all that is needed to be tracked, if it comes back up then its static will be advertised again and take preferance/

res

Paul

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Thanks.

[jawad-mukhtar]

agreed.

just for isplsa monitoring if track goes up and down u can recieve messages in syslog.

Jawad

[ravi mishra]

thank you for the post,just a doubt.

can  ip sla be implemented in a L3 switch or is it that we can just monitor it from the switch level ?..and can we use BGP instead, to provide solution for this?

because it seems not working in packet tracer.

thanks

[paul driver]

Hello

Yes a L3 switch is able to perform the above function - and yes bgp  can also be used to connect to your ISP.

It all depends on your requirements in terms of routing updates to and from your service provider, if you need the full Internet routing table, then you most probably require a higher specification L3 switch/router to accommodate this and obviously bgp to receive them.

However if you dont require any routing updates, then BGP or any IGP is not necessary and static defaults can provid a much simpler design

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.