Multilink PPPoE Scalability Issue

[Sarpreet <sar () knowledgecomputers net>]

Please help :)

The network topology is:
  ADSL CPE (Cisco 2800)  +===[PPPoE]===+  LAC (Telco's equipment) 
+===[L2TP]===+ LNS (Cisco 7513)

The setup is for aggregating multiple PPPoE DSL lines with PPP.  Using 
the Cisco 7513 as the LNS, the setup works up to 15 MLPPP bundles and 
with Cisco 7200-NPE400 only works up to 5 MLPPP bundles.  After that, 
additional MLPPP bundle attempting to connect won't be able to complete 
IPCP phrase--the L2TP tunnels are created, each individual PPP link 
members are up, and the MLPPP bundle is created, just cannot finish the 
IP "handshake" part of the IPCP phrase.  In fact, even a normal PPP 
(without Multilink) session won't be able to complete the IPCP phrase as 
long as there are 15 active working MLPPP bundle is on.

I have search through Cisco's website to see if there is any documented 
limitation/restriction on the number of bundles the 7513 can support.  
The closest thing I can find is an reference to a 7500 w/ VIP4-80 can 
only support a limited number of T1 MLPPP bundles ( 
http://www.cisco.com/en/US/docs/ios/12_0t/12_0t3/feature/guide/multippp.html#wpxref1033494 
).


Cisco 7513 spec:
  Cisco IOS Software, RSP Software (RSP-JSV-M), Version 12.4(21), 
RELEASE SOFTWARE (fc1)
  Cisco RSP8 (R7000) processor with 262144K/8216K bytes of memory.
  R7000 CPU at 250MHz, Implementation 39, Rev 2.1, 256KB L2, 2048KB L3 
Cache
  Last reset from power-on
  Chassis Interface.
  1 FEIP2 controller (2 FastEthernet).
  2 FastEthernet interfaces
  2043K bytes of NVRAM.

  62720K bytes of ATA PCMCIA card at slot 0 (Sector size 512 bytes).
  16384K bytes of Flash internal SIMM (Sector size 256K).

Cisc 2800 spec:
  Cisco IOS Software, 2800 Software (C2800NM-ADVIPSERVICESK9-M), 
Version 12.4(15)T3, RELEASE SOFTWARE (fc1)
  Cisco 2811 (revision 53.51) with 247808K/14336K bytes of memory.
  Processor board ID FTX0945A4WJ
  2 FastEthernet interfaces
  3 ATM interfaces
  1 Virtual Private Network (VPN) Module
  DRAM configuration is 64 bits wide with parity enabled.
  239K bytes of non-volatile configuration memory.
  62720K bytes of ATA CompactFlash (Read/Write)

----------- Relevant CPE config: -----------------
interface ATM0/0/0
no ip address
no atm ilmi-keepalive
dsl operating-mode auto
pvc 0/33
tx-ring-limit 3
vc-hold-queue 80
pppoe-client dial-pool-number 1
!
!
interface ATM0/1/0
no ip address
no atm ilmi-keepalive
dsl operating-mode auto
pvc 0/33
tx-ring-limit 3
vc-hold-queue 80
pppoe-client dial-pool-number 1
!
!
interface Dialer1
mtu 1486
ip address x.x.x.1 255.255.255.0
encapsulation ppp
dialer pool 1
no keepalive
no fair-queue
no cdp enable
ppp chap hostname abc () smarttadsl com
ppp chap password highlysecretive
ppp pap sent-username vaamadsl () smarttadsl com password highlysecretive
ppp link reorders
ppp multilink
ppp multilink fragment disable
!
ip route 0.0.0.0 0.0.0.0 Dialer1



----------- Relevant LNS config: -----------------
aaa authentication ppp default group radius
aaa accounting network default start-stop group radius

vpdn enable
!
vpdn-group 1
! Default L2TP VPDN group
accept-dialin
protocol l2tp
virtual-template 1
lcp renegotiation always
l2tp tunnel password faketunnelpass
ip mtu adjust

interface FastEthernet8/1/0
description Facing-LAC
ip address y.y.y.5 255.255.255.252
ip tcp adjust-mss 1446
full-duplex
fair-queue
!
interface Virtual-Template1
ip address x.x.x.254 255.255.255.0
no peer default ip address
no keepalive
ppp mtu adaptive
ppp authentication pap
ppp link reorders
ppp multilink
ppp multilink fragment disable
!


Sarpreet Basi
Knowledge Computers
sar () knowledgecomputers net