Is it recommended to use HSRP or multiple default between Core Layer Switch and Customer Edge Router?

[Mahesh Deshpande]

My client is asking me for following

Client is using Router as edge device. 2  WAN links from different service provider ( each 20 Mbps)  are getting terminated on the router. There are internal servers present in the network. Client want to make setup such that even if one wan link fails  internet users should be able to access web server. Moreover if the edge router fails there should be secondary edge device so that there is device redundancy ?

As per my understanding, in this scenario we need to do static one - to - one natting(belonging to WAN interface subnet). If we use two routers as Customer edge ans if we connect core layer switch to these two router, is it recommended to use HSRP/VRRP/GLBP or two default route on core switch pointing to two routers with equal ad value. we will also track the wan link with help of ip sla.

which is recommended solution  Router redundancy protocol or Default routes.?

[Jon Marshall]

Ideally your SP would provide default routes then you can pass these back to the L3 switch and there is no need  for IP SLA but for that you need to have a dynamic routing protocol running between you and the SP (usually BGP).

So assuming you can't do that I would go with using L3 links to the routers.

Personally I think HSRP etc. is primarily for end devices. So,as I say, I would connect the routers with L3 links and have a default route pointing to the primary which you track and then a floating static route pointing to the secondary which is installed in the routing table if the first is removed.

If you use HSRP this adds complexity. If you IP SLA is tracking an IP within the SP or the internet then if it fails your HSRP active router is still up. Your default route is pointing to the HSRP VIP. This route is removed and the other one is installed but this is also pointing to the HSRP VIP so the traffic still gets sent to the primary router which isn't what you want.

HSRP would be useful if there wasn't a L3 switch ie. your clients default gateway was actually the HSRP VIP but because you have a L3 switch you don't have this setup.

Jon

[Jon Marshall]

Just had another read of this post and some other points have come up.

1) I assumed your secondary link was for redundancy but you talk about terminating both SP links on the same router in your first paragraph.

Did you mean this or are you going to be terminating a link per router ?

2) are you using the second router purely for backup ?

3) something you didn't ask about but is relevant is the IP addressing. Are you using provider independent addressing or does each SP provide you with an address block.

If it is the second then you are going to have an issue with the web server. The problem is which provider's IP do you use for the web server ie.

if you use the primary provider IP then that will be the DNS record on the internet. If the primary router fails then the IP address will change on the secondary router but DNS will still be handing out the primary IP.

If you enter both IPs (primary and secondary) into DNS then you would get load balancing but this means both links will be used and the secondary would not just be backup.

In addition if one of the links fails then DNS does not know this so it will still be handing out the failed address as well as the address that is still up which means some connections will work and some won't.

Jon