Virtual-Templates Limitation on 7606

[2012jakejake]

I have a requirement of terminating PPPoE session from the CPE on individual Virtual-Templates. But with the current IOS c7600rsp72043-advipservicesk9-mz.122-33.SRD2a.bin on a 7606 the maximum number of virtual-templates that it supports is  200. Is there anyway of extending that limit with an IOS upgrade? Also any idea on the limit of Virtual-Template on 7200/ASR 1000 series routers and will there we any impact on performance if high number of VT's are created?

[Preston Chilcote]

The number of configurable virtual templates can not be changed via cli. However, it does differ per platform and sometimes IOS version. For example, this bug increased the number to 1000 for RSP270:  CSCtf20154    set MAX VTemplate to 1000 for 7600 RSP720   You can upgrade to 12.2(33)SRD5 to allow you to configure up to 1000 virtual-templates.  This limit for 7200 has been 1000 for quite awhile, so most IOS versions should be that way.  The limit for ASR1k is 4095 and I think it's been that way since the product launch.  Nothing is for free, so there will be some performance impact for adding more interfaces, but it would most likely be limited to higher cpu utilization, which you can monitor with "show process cpu".   I don't think you'll run into many issues though unless the cpu is already really high.  The 7600/rsp720 can scale to tens of thousands of pppoe sessions, but only if you use a small number of virtual-templates and rely on cloning virtual-access sub-interfaces.  This reduces the system resources required for handling so many interfaces.  I think that would be the optimal design if it's possible in your network.

[2012jakejake]

Thanks for the info. Can you share some info with regards to 7200 router?

[Preston Chilcote]

It's buried in my reply.  The limit on 7200 is 1000 virtual-templates.

[2012jakejake]

Further to the above query, is there any possibility to enable dynamic routing protocols on Virtual-templates/virtual-access in a DSL environment where the DSLAM connects to an Ethernet backbone.

[Preston Chilcote]

It is possible, but you want to make sure that the virtual interfaces are passive (passive-interface default under the routing protocol configuration) so that the router isn't trying to send hellos on hundreds of virtual interfaces.  If you are simply trying to get the subscribers routes into your routing table, I would favor just redistributing a static route for those networks to reduce the overhead of having a routing protocol keep track of each subscriber.

[2012jakejake]

I assume Virtual interfaces being referred is virtual-templates... The reason I am looking for dynamic protocol is since there will be two PE routers the CPE will connect to for redundancy..

In a scenario where a CPE homes to two PE router through a single vlan, the CPE will connect to either one of the PE router which ever replies to the PPPoE request... Is there anyway of preferring request from either one of the PE routers?

[Preston Chilcote]

Generally the CPE (pppoe client) will accept the first PADO response it gets from the BRAS(es).  There is a bit of natural load balancing that happens, because the "busier" BRAS will probably take a little longer to respond.  However, there is a newer feature called PPPoE Smart Service Selection that allows for a little tuning as well:

http://www.cisco.com/en/US/docs/ios/bbdsl/configuration/guide/bba_pppoe_sss.html