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?
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.
randy
Randy Bush wrote:
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.randy
Does it count as multihoming when we are the only ones announcing the space?
It's been my experience that many providers do not care what address is used
for sourcing traffic. This is why it is not uncommon to see traffic sourced
from RFC1918 space coming across various providers networks. If more
providers adopted BCP 38 this wouldn't be a problem, but that doesn't seem
to be happening anytime soon...
I'd try to identify which providers the customer is connected to and take it
from there...
Stefan Fouant
www.shortestpathfirst.net
GPG Key ID: 0xB5E3803D
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?
randy
or maybe just better pricing on the other provider, and that provider
offers something akin to 'no-export' (or maybe they just used
no-export).
-chris
Hi,
Are they complaining about somehting? If so, ask for a traceroute.
You might also try calling and asking. "We're seeing some strange
traffic purporting to be from your addresses but not coming from your
circuit. We're concerned that someone might be attacking your network.
Before taking action to protect you, we want to eliminate the
possibility that you have a second ISP through which you're
accidentally sourcing the packets."
Beyond that, what's your game plan once you know the answer? Threaten
to cut them off? That's a great way to lose a customer who you know
*already* has a second ISP. Maybe you'll call their second ISP and
complain about their filtering practices? I'd love to get that call
from you. Tells me exactly which name to pass to my upsell specialist.
Yes Mr. Customer, your other ISP is trying to cut you off. They even
asked us to block your packets. But for just a little more we'll give
you IP addresses that you can use with any ISP.
Regards,
Bill Herrin
I've had two customers pull this stunt in the past with me - one, a spammer, tried to do this with an ADSL modem from me, the other (a non-spammer with a clueless 'consultant') had a T1 from me and a T1 from UUNet.
It started with the T1 customer. I believe they had a smaller block of IPs (less then /24, more like a /25 or /26), and their 'computer consultant' with his infinite wisdom decided to send all outbound traffic through the UUNet T1 rather then source routing which we highly recommended to them. Of course, we had ingress filters in place to block IP ranges we have from coming into us from the WAN links, so when they tried to contact servers on the other half of the netblock on our end, the connections mysteriously failed. After lying up and down that it was our fault, that their computer 'consultant' was regarded as best in the country, blah blah blah, we flipped on logging on the ingress filters out of sheer curiosity and discovered exactly what was going on.
The ADSL customer was a bit more tricky - we were getting spam reports about his single IP address sending spam, but we had his outbound port 25 blocked. Ended up sniffing the port off the router he sat off of, and discovering that it was all one sided, wasn't even tickling the ingress filters.
Hey, at least your customer didn't convince AT&T to allow them to announce out one of your /24s when all they had was a /29.
Your in a tricky bind, I'd approach them under the guise of ingress filtering issues.
Brielle Bruns wrote:
(Forgive the top posting, stupid blackberry can't do inline)
A creative idea that I did in a test lab one time - stateful connection tracking, its not just for NAT you know.
Would require a bit of moving stuff around and reengineering of your connection to them, but it would cripple their connection unless it originated through you.
IE:
You <-> UNIX/Linux firewall <-> T1/eth/dsl/etc
If stuff went out the other way, it would come in, firewall says WTF, and drops it because it didn't see the initial SYN exchange.
My partner Tammy says a PIX could probably accomplish the same task (we have some here for the corp lan stuff, including spares).
Brielle
Yes, a PIX/ASA would stop this cold. The TCP state tracking would not
allow traffic to pass unless the whole 3-way handshake was observed by
the box. Only recently did Cisco add features to make tracking the
TCP connection state optional.
(http://www.cisco.com/en/US/docs/security/asa/asa82/configuration/guide/conns_tcpstatebypass.pdf)
The larger ASA-5580 machines can be virtualized into dozens (or more)
security contexts as needed. I imagine it would take some effort to
figure out how to cleanly integrate such a configuration into a POP.
--D
What trouble? SMTP requires two-way traffic with a static port number
that nothing else uses. If for some reason you don't want to simply
terminate their account altogether, block packets outbound to your
customer sourced from TCP port 25 but not from your SMTP smarthosts.
Seriously though, if you can prove they're spamming (regardless of
whether the packets pass through your network) save yourself some
grief and just terminate the account.
Regards,
Bill Herrin
Brielle is correct. The customer in question is spamming networks and
we are having trouble filtering them because another provider allows
them to source traffic however they please.
then perhaps the issue is a bit larger than their traffic incoming to
you. disconnect the schmucks.
randy
Yes - term the account would be my recommendation
And if you filter port 25 traffic do it both ways
Read these old nanog threads ..
http://www.irbs.net/internet/nanog/0408/0465.html and
http://www.mail-archive.com/nanog@merit.edu/msg28863.html
Brielle is correct. The customer in question is spamming networks and we
are having trouble filtering them because another provider allows them to
source traffic however they please.
If they are spamming just pull the plug, whatever revenue you get from them
is not worth your reputation and caring for other good customers, and the
rest of us will speak highly of you for taking another spamcrock out
of the net.
Cheers
Jorge
Actually, this can be achieved easily using reflexive ACLs on any Cisco
router, so no real need to change the topology or add new devices in the
path:
http://www.cisco.com/en/US/products/sw/secursw/ps1018/products_tech_note09186a00800a5b9a.shtml#reflexacl
Arie