[sdnog] Hot standby routing protocol (HSRP)

[Nishal Goburdhan]

On 5 Jan 2016, at 10:44, Sara Alamin wrote:

> Hi All.
> Happy New year , Wish you all the best :)
> Today I was reading about interesting topic and it was new for me it 
> is : HSRP.
>
> What will happen if you lost your gateway?how can you access the 
> internet ?Can you Configure your PC or your servers with multiple 
> gateways? how can you provide a backup gateway for your customers?...
>
> Hot standby routing protocol (HSRP) sets up a virtual IP address 
> between two routers (could be more) to provide layer 3 fault tolerance 
> for customers using a default gate way.
>
> you can find more: https://www.ietf.org/rfc/rfc2281.txt
>
> and here is a small video to show you the general concept:
> https://www.youtube.com/watch?v=kxhdPI1jh6I
>


hi sara,

and happy new year to you (and the list).

it’s worth mentioning that hsrp is a proprietary cisco standard;  the 
open-standards based version of this, is vrrp.  see 
http://www.ietf.org/rfc/rfc3768.txt.  so, if you’re not using cisco 
equipment, you’d use vrrp, instead of hsrp.  operation and 
configuration is pretty similar.

remember, that this is an excellent tool to use for *client* facing 
networks;  so in an office lan, or on a client-hosted subnet, where the 
users of the “default gateway” are typically “dumb” 
computers/tablets/phones/etc that do not necessarily know how to deal 
with multiple default gateways, or path selection.
it’s typically not something that a provider would use in their 
backbone;  routers are “smarter” and use routing protocols to 
achieve resiliency.

in an environment where you would want to think about resiliency, i 
generally recommend that you setup and do this, even if you have one 
router, since, adding in an additional router as part of the hsrp/vrrp 
group later, can be down seamlessly, and with no downtime.  for example, 
at sdnog-2, we did this, even though there was one border router :-) and 
a chance that we might get one later…

also remember that this does eat into you IP address allocation as well; 
  instead of a single ip address as the default gateway, you now need 
probably three.   that’s a small price to pay for more sleep though!  
:-)

—n.