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TheSmallOne
Guru
Joined: 22 Jan 2005
Posts: 467
Location: Germany
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 Posted: Sun Jan 03, 2016 12:37 pm Post subject: Binding loopback-address to non-loopback interface |
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Hi,
recently I've seen a system, on which there were several loopback addresses configured on normal interfaces (like 127.0.0.1/32 on eth0 and 127.0.0.2/32 on eth1).
The first question which comes to mind is: Is this even a legit configuration?
And then I wonder, what exactly can be gained by adding loopback addresses to normal interfaces.
Has anybody seen a similar configuration and has in idea, what exactly this is supposed to do? |
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UberLord
Retired Dev
Joined: 18 Sep 2003
Posts: 6835
Location: Blighty
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| Posted: Mon Jan 04, 2016 10:04 am Post subject: Re: Binding loopback-address to non-loopback interface |
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| TheSmallOne wrote: | Hi,
recently I've seen a system, on which there were several loopback addresses configured on normal interfaces (like 127.0.0.1/32 on eth0 and 127.0.0.2/32 on eth1).
The first question which comes to mind is: Is this even a legit configuration?
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Yes.
Saying that, 127/8 isn't supposed to leave the host regardless, so there should also be a reject route for that subnet to remain RFC compliant.
| Quote: | And then I wonder, what exactly can be gained by adding loopback addresses to normal interfaces.
Has anybody seen a similar configuration and has in idea, what exactly this is supposed to do? |
It could very well be that the lo (lo0 on BSD) interface doesn't actally exist.
It doesn't have to either.
However, you lose a lot moret than you gain because loopback interfaces normally have a very large MTU value so no fragmentation ever occurs whereas it will on the interface even if you're talking to the same address.
This is why modern OS's add a route to each IP address via the loopback interface.
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