Router - Cisco 887VA PPP Settings

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The following is from a customer with a Cisco 887VA:

I'm using a Cisco 887VA with your VDSL2 service. I've had an issue where the session would bounce several times before coming up stable. I thought it was an IPv6 issue, as between bounces, v6 wasn't being passed but v4 was. Turns out something was failing just before v6 got negotiated.

During a failed session, "debug ppp nego" revealed:

Vi2 PPP: Control packet rate limit 10 reached

Followed by lots of dropped/throttled PPP packets. Turns out the default (for IOS 15.4(3)M1 at least) is to allow 10 PPP control packets per second. After that it throttles them for 30 seconds and misses a load of keepalives, whereupon it drops the session. That rate limit was probably fine in the past, but more stuff gets negotiated now (e.g., IPv6) and I guess the line rates of VDSL means it all happens quicker too.

For me, that repeated a few times until it happened to get through the whole process - generally taking 5–10 minutes to get a stable session. I guess some control packets get delayed every now and then just enough to not trigger the throttling. I only have the 40M service - maybe with 80M it would never have come up! (Pure speculation)

Anyway, customer-side fix is simple:

# ppp packet throttle 20 1 30

Doubles the amount of ppp control packets allowed per second, backoff stays the same.