[c-nsp] ASR1000 - Software Redundancy

[Mark Tinka]

On Tuesday, January 31, 2012 11:38:53 PM Antonio Soares 
wrote:

> The box has 4 GB of memory but the IOSd only allocates
> 1,7 GB. Is this dynamic ? How do we control this ?

We turned on software redundancy on our ASR1002's a couple 
of years back, while they were running at least 3x full BGP 
feeds. This was still on IOS XE 2.6.

Over several weeks, the box run out of memory and crashed. 
We traced the issue back to the software redundancy + large 
memory consumption due to BGP routing.

We disabled software redundancy and have never turned it on 
since. If we want control plane redundancy, we buy the 
ASR1006, which is one of the reasons we never buy the 
ASR1004. Only the ASR1002 (size, cost) and the ASR1006 
(redundant, high capacity).

If you have 4GB DRAM in the router, IOSd itself will take 
2GB and the other 2GB will be used for internal purposes. If 
you have SSO turned on for software redundancy, the 2GB that 
was allocated to IOSd will be halved further to 1GB for the 
native IOSd, and another 1GB for the redundant IOSd. 
However, other internal processes would consume memory from 
the remaining 1GB of the native IOSd, leaving with you about 
600MB - 700MB of free memory on that partition.

Now throw a couple of full BGP feeds into the remaining odd 
700MB, and you quickly see what is wrong with this picture.

There is a caveat (unofficial) that Cisco do not recommend 
running software redundancy if the router is running BGP. 
You won't find this recommendation online anywhere, as it 
was an internal discussion within the ASR1000 BU. But AFAIK, 
internal notes have been made available to account teams in 
case customers have questions about this.

Bottom line, don't enable software redundancy if you have 
BGP running. Personally, I don't enable software redundancy, 
period. I bought a box with a single control plane. If I 
want redundancy, I'll buy one with two control planes.

The idea is novel, but it doesn't really work.

Hope this helps.

Cheers,

Mark.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: This is a digitally signed message part.
URL: <https://puck.nether.net/pipermail/cisco-nsp/attachments/20120201/0aa06ed0/attachment.sig>