Finding asymmetric path

Joe Greco jgreco at
Sat Nov 28 15:41:09 UTC 2009

> >>> I'm reasonable certain a customer of ours who is using one of our 
> >>> netblocks is using a different reverse path to reach us.  How might I 
> >>> figure out who is allowing them to source traffic from IPs that belong 
> >>> to us?
> >> you are implying that they are not allowed to multi-home using the ip
> >> space you have assigned to them.  good way to lose a customer.
> > Does it count as multihoming when we are the only ones announcing the
> > space?
> almost an interesting question.  but i think it is playing with words.
> if i understand your original statement, they are clearly attached to at
> least two providers.
> perhaps it is fear of what they, possibly mistakenly, perceive to be
> your policy regarding announcement of space that keeps them from
> announcing normally to both, or more, links?

It could also be something simple like pricing.  For example, in a large
colo facility, you might easily find that a number of providers offer
low cost transit, but not IP space.  For a customer who is heavy on the
outbound traffic, they might find it more affordable to buy their inbound
plus IP space from you, and then dump onto Cogent or something like that
for outbound.  Unless your contract specifically prohibits this, you're
probably not going to be able to prevent it.

... JG
Joe Greco - Network Services - Milwaukee, WI -
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.

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