[c-nsp] NSR and GRES

[Mark Tinka]

On Sunday, February 27, 2011 08:04:04 am David water wrote:

> Any good documentation on NSR or GRES that some one can
> point me to? 

GRES would be more appropriate on the 'j-nsp' mailing list, 
as that's Juniper terminology.

The equivalent on the Cisco side is SSO.

> I am looking for the functionality and
> design recommendation?

It mostly comes down to protocol support and maturity.

Graceful Restart (what Cisco call NSF) has greater protocol 
support and is generally considered more mature. However, it 
requires co-ordination with other routers in the network 
(different modes for those with only one control plane and 
those with two) and is a little slower compared to NSR.

NSR has generally lagged behind re: protocol support, but 
this has been changing in the last 18 months or so, and most 
major protocols should now be supported. 

You'll probably find more networks running Graceful Restart 
rather than NSR, but I'm sure NSR take-up is mounting.

NSR makes more sense if you're looking for more hitless 
failovers (it's faster since state is active across both 
control planes). But some vendors have had strange bugs when 
NSR is deployed. YMMV. Test, test, test.

One of the fears in the past was that whatever caused the 
primary control plane to fail would propagate to the 
secondary one during a switchover, causing it to fail as 
well, when NSR is used. I'm not sure how relevant that still 
is today - we've mostly been a Graceful Restart shop here.

> What IGP timer should I use with
> it? OSPF Fast hello will work with NSR and GRES?

Try BFD, along with Graceful Restart or NSF, depending on 
what your platform supports.

Cheers,

Mark.
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