Subject: BGP PW inter-provider scalability for VPLS

From: [email-masked]
Date: Tue, 17 Jun 2003 09:00:35 +0100

I have a couple of questions regarding the scalability of the VPLS BGP
signalling draft. It seems to me there are two VPLS scaling issues regarding
signalling in the inter-provider case:

i)  Number of BGP/LDP sessions
ii) Number of PWs

The BGP signalling draft addresses the first issue as service providers can
use route reflectors with EBGP sessions between them (option C from
rfc2547), however it does not address the second issue. For example, lets
say we have an intra-provider network (SP1) with 800 customers, each of
which have an average of 10 fully meshed VPN sites, the number of
intra-provider PWs required would be:

= m(n*(n-1)/2) - where m is the number of VPLS instances and n is the number
of PEs
= 800(10(10-1)/2)
= 36,000 PWs

Now lets say SP1 wanted to connect  to another provider (SP2) to create an
inter-provider service, and that 200 customers want to connect their 10
sites in SP1s network 10 sites in SP2s network in a full mesh giving a total
of 20 sites. The number of PWs required would be:

= m(n*(n-1)/2)
= 200(20(20-1)/2)
= 38,000 PWs

Of these 38,000 PWs, some are SP1s intra-provider PWs, and some are SP2s
intra-provider PWs. SP1s intra-provider PWs can be calculated using:

= m(n*(n-1)/2)
= 200(10(10-1)/2)
= 9,000 PWs

The calculation for SP2s intra-provider PWs gives the same number (9,000),
which means the total number of inter-provider VPNs required between SP1 and
SP2 is: 38,000 - 9,000 - 9,000 = 20,000.

So, in the inter-provider case, SP1 must now provision and manage its
original 36,000 intra-provider VPNs, plus 20,000 inter-provider PWs. This is
just over a 55% increase in the number of PWs to provision and manage, even
though only 25% of SP1s customers have inter-provider VPNs.

The LDP VPLS signalling draft addresses this issue by defining a
hierarchical model in which two fully meshed VPLS networks are connected
together using a single LSP tunnel between the VPLS gateway devices. In the
above example, only 200 PWs would be required between the two gateway PEs,
as opposed to the 20,000 fully meshed PW in the BGP case. The LDP
hierarchical model also addresses issue i) regarding the number of sessions
required as only one LDP session is required between gateway sites.

Although the hierarchical model may not be without its own problems (e.g.
the issue of gateway PEs having to perform MAC address learning when
connecting to multiple ASs has been brought up) it does address the problem
regarding the number of PWs required. 

Questions:
==========

I would be grateful if anyone can help with the following:

1. Are there plans to address the number of PWs scaling issue in the BGP
VPLS draft? (Or perhaps this is addresses in a separate draft and I've
missed it?)
2. I would also be interested to know what people think the biggest problem
in the above example would be: a) MAC address learning at the gateway PE for
200 PWs, or provisioning and managing an extra 1,800 PWs.

Thanks,

Richard

---

From: [email-masked]
Date: Tue, 17 Jun 2003 12:12:00 +0100

Having thought about this properly, option A or B from RFC2547 could be used
instead of option C to reduce the number of PWs required. I guess the only
question that remains is what's more important (i) reducing the number of
inter-AS PWs at the expense of placing a heavier workload on the gateway
devices, or (ii) using RRs with EBGP sessions between them to reduce the
workload on ASBRs at the expense of increasing the number of inter-AS
PWs?...

Richard

 > -----Original Message-----
 > From: [email-masked] [mailto:[email-masked]]
 > Sent: 17 June 2003 09:01
 > To: [email-masked]
 > Subject: BGP PW inter-provider scalability for VPLS
 > 
 >