Re: [PROBLEM] No ARP answer when two ifaces with same IP exist (2.2.x)

Alan Cox (alan@lxorguk.ukuu.org.uk)
Sun, 29 Aug 1999 17:04:47 +0100 (BST)


> Alan, patches floating around and including different checks
> for IFF_NOARP, IFF_UP, calls to ip_dev_find() etc. are wrong.
> They break more things than repair.

Of that Im sure

> I do not understand the problem for now and, hence, cannot react
> more constructively.

The ipvs folks are doing IP level load balancing with inverse masquerade
-ie

internet
|
[MASQ]
+------+--------+-------+-------+------+
www1 www2 www3 www4 www5 www6

incoming SYN frames create masquerade sessions mapping user->www to user->www1
www2, etc according to load and rules.

In one mode they set things up differently as follows

internet
|
+-----+-----+-----+-----------+----------+---------+
| | | | | | |
MASQ www www www www www www
www1 www2 www3 www4 www5 www6

Each host is www and a unique name. The masq host arps for www, then
tunnels the packet to a www[1-n] but without rewrite. The reply doesnt touch
the masq so is a lot faster.

However they need to stop www1->wwwn arping for their www tunnel address

Alan

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