UK BT ADSL2+ Annex A - Cisco 877 - Page 4

Ian Cowley · ‎10-10-2009

UK is currently going through a nationwide migration from ADSL, ADSL2 and ADSL2max to ADSL2+.

Most British Telecom (BT) MSANs are configured for Annex A, though we know that some LLU suppliers are using Annex M (with UK mask) which Cisco currently doesn't support.

Our issues are that all out Cisco 877s and there are 100s deployed that are subject to a line upgrade, or a new installs on ADSL2+ fail.

We have used the latest IOS that will runn on the older 128M DRAM units 12.4(15)T11 I think, and 12.4(24)T1 on newer units. We have also played with DSL Modem firmware 3.0.33 and more recently 4.0.015 (which incidently works very well on UK ADSL2 Annex A). None have helped.

The connectivity in UK is PPPoA

Symptoms:

It appears to be dependent on the amount of data through the DSL interface.

So a 24Mb/s connection will fail in hours, whereas a 9Mb/s will fail in days.

'sh int atm0' will show drops

'sh buffers' will show the middle and big buffers failing in particular.

Small packets such as ICMP and SSH will continue to work, so we can log on to the router(s) remotely.

But large packets such as those used for normal data will not pass the router reliably if at all.

Replace the router with a $100 item and the connection speed is normally better and there are no issues.

All these routers are similarly configured, have CBAC inspect code and a single IPSEC VPN.

MTU and MSS sizes are reduced to support IPSEC.

(though I hear the same problem from other UK deployments)

I have placed some info on the NetPro forum, seach for ADSL2+ and you should find it.

I have calls out to BT, large UK distributors and ISPs without any resolution or identification of the problem.

I think this is a significant issue given the value of Cisco DSL real estate in UK.

HELP!!!!

Ian Cowley

mcreilly · ‎06-20-2012

Is this one of the longest-running threads on the forums?

I have an 877W with the same problems. It was rock solid for 18 months when used with ADSL Max ("up to 8Mb") service. I'm lucky to live in a newly built street not far from the BT exchange with shiny new cabling all the way, and was reliably getting a perfect 8Mb down/832Kb up all the time.

But then I asked my ISP (PlusNet) to upgrade me to ADSL2+ Annex M.

Initially it connected at 12M down, 3M up. Nice. Then within hours the frequent disconnects had BT knocking the speed down, and down, and down, so I was on 4Mb down/512k up,

I'm on firmware 3.0.33, I tried 4.0.18 but it was no better (possibly worse). I just bought a SmartNet contract for this router to get TAC access to obtain the more exotic releases mentioned in this thread to see if they help.

Copying the .bin file to flash (renamed appropriately) and rebooting doesn't always seem to cause the firmware to be loaded though - sometimes it loads, sometimes a "sho dsl int atm0" says it's using the 3.0.33 included in the IOS.

As others have mentioned, it's highly frustrating that a high end router (as home routers go) has such problems when a £30 Linksys device seems to cope better!

Nik Warren · ‎06-20-2012

I had the same issue over a year ago. I managed to fix this by changing the TX-Ring-Limit.

I did this under the ATM0 interface. It has never failed since.

interface ATM0

no ip address

no ip mroute-cache

logging event atm pvc state

logging event atm pvc autoppp

atm vc-per-vp 64

no atm ilmi-keepalive

pvc 0/38

tx-ring-limit 3

encapsulation aal5mux ppp dialer

dialer pool-member 1