[c-nsp] IPv4/v6 Route Reflectors - Which router to choose?

[Mark Tinka]

On Friday 11 June 2010 08:11:17 pm Jonathan Hart wrote:

> I have a question relating to IPv4/v6 route reflectors in
>  SP environments. My question isn’t so much about BGP and
>  the actual RR functionality, as it is about the “right
>  kind of router” for the job. What kinds of qualities are
>  important, except for feature support, when looking at a
>  suitable RR? I am not looking for very detailed answers
>  – just a general guideline to follow.

	- Lots of control plane memory, not so much forwarding
	  performance (unless you intend to have your route
	  reflectors handle user traffic as well).

	- Lots of CPU.

	- Comprehensive BGP feature set.

	- Relatively inexpensive box.

We've been very happy with the Cisco 7201 router, save for 
two small issues:

	- No support for RFC 4684 in IOS, even though I've been
	  pressing Cisco for it since '07. Another vendor supports
	  this.

	- No support for MCAST-VPN NLRI if you're into NG-MVPN's
	  and need route reflection for that. Another vendor
	  supports this (at any rate, Cisco have a different
	  philosophy re: advances in Multicast routing/forwarding).

The 3rd issue, well, we really can't complain about since 
it's one of those Kompella vs. Kompella problems re: LDP vs. 
BGP for point-to-point l2vpn's. Since the BGP-model isn't 
in-line with Cisco's ideals, they have no plans the draft 
that defines it.

However, after a little bit of instability in initial code, 
the 7201's will happily reflect VPLS BGP NLRI between IOS 
and JUNOS. Cisco support this model.

But I digress...

> I noticed that Cisco had put ASR1002 on the candidate
>  list for BGP RR
>  (http://www.cisco.com/en/US/products/ps9343/index.html).
>  While the ASRs are powerful and mighty, they seem to be
>  somewhat over the top for the job.

If you're going to consider this platform, the ASR1002-F is 
probably a cheaper option. In many ways, it was designed for 
such deployments.

Otherwise, I'd highly recommend the 7201 with SRE (you'll 
want that 4-byte ASN support). I've only used IOS XE in an 
edge role, so haven't yet worked out any kinks re: the BGP 
implementation when used in a route reflector role.

>  It also seems like
>  the 7200/7300, even the 7600 platform is normal to find
>  as RRs too.

I'd avoid the 7600 since it's also too big. The RSP720 is 
faster than the SUP720, but I've seen the 7201 perform 
better when handling BGP.

We have our 7201's handling several tens of routers and a 
couple of full feeds (v4 and v6) idling at 2% CPU. The 
network is doing several Gbps of bandwidth everyday.

> My understanding is a router to be used as RR should
>  have;
> 
> ·         Adequate memory to support the routing table.

Yes, in the control plane since a dedicated route reflector 
won't be forwarding any user traffic.

> ·         Basic feature support (BGP, MPLS, etc..)

MPLS isn't necessary (the IGP will handle reachability 
between the route reflector and all iBGP speakers). In fact, 
we had to disable MPLS on our route reflectors as they were 
attracting traffic that saw them as part of the LSP path.

Also, enabling the Overload bit in IS-IS ensured they never 
handle any data plane traffic (good knob, that).

BGP support should not be basic, as route reflectors is 
where a lot of your routing policy could be held/enforced. 
You want to have as many (stable) BGP features as you can 
get.

> ·         Moderate forwarding power – bandwidth doesn’t
>  seem to be that important.

Again, not if you plan to have a dedicated route reflector. 
The only traffic it needs to forward are BGP/IGP/control 
plane updates and management plane traffic.

> How would the upper end for the ISR G2 routers perform as
>  IPvXrrs? The 3925s, 3945s, etc.

Never used these, but I know a friend who was happy running 
hundreds of thousands of v4 routes on a 2851 back in the 
day. I've used a 2851 as a route reflector, but handling 
only a single full v4 feed and a couple of iBGP sessions. 
CPU idles at 3%. No major dramas.

They certainly have the RAM, but not sure what their CPU can 
do in times of need. So the more current ISR's would be 
marginally better in performance, although I'd still be more 
comfortable with a 7201.

Cheers,

Mark.
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