[nSLUG] Problems with Eastlink Hosting Multiple IPs on One Network Interface

Jonathan Freedman rewt at eghetto.ca
Tue Nov 15 11:38:26 AST 2005


Ok. As I'm sure most of you know, cable modem networks are treated as
huge "logical" local area networks. hence the hella arp requests. now what
most of you might not know is that each modem is actually an embedded
system which does quite a bit of filtering. the outgoing port 25 filter,
for example, is blocked right at your modem. the non-arp packets for
everyone else on this "LAN" is blocked at the modem as well.

now for the broken alias stuff... i have been running anywhere from two to
four IP's aliased on a 2.4.x based linux firewall for two years now
without any issues. i had to get into policy routing at one point, but
that's another story. it sounds like what the eastlink tech told you is
true with their arp tables having troubles updating. you can try asking
them to set static arp entries. if they refuse, try calling back and ask
for someone else.  good ol' call centers.




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