ip route show cache

KatrinAlec · 11-04-2022, 09:51 AM

Two questions:

I thought that the routing cache didn't exist any more, but I found it in Debian Bullseye.
So there is a routing cache again?

Now I'm wondering why does the routing cache show lots of entries for exactly the same source and destination.
Does every SYN put an entry into the routing cache? If so, why do all the entries for the same source and destination have the same expiry time?

IsaccBarker · 11-07-2022, 05:50 AM

Yeah, it was removed in 3.6, I think. It had a really bad performance and security issues. Its average hit rate was around 10%. Source.

According to the man page,

Quote:

Starting with Linux kernel version 3.6, there is no routing cache for IPv4 anymore. Hence ip route show cached will never print any entries on systems with this or newer kernel versions.

It doesn't mention anything about the IPv6 cache being absent, is that what you are seeing? What command are you using to view the cache?

As for the same source and destination address, I have no idea.

KatrinAlec · 11-07-2022, 07:28 AM

Kernel is > 3.6

Quote:

uname -r
5.10.0-17-amd64

and I use
ip route show cache

right now it has 8546 lines with entries like

Quote:

x.x.x.x via y.y.y.y dev gre2
cache expires 401sec mtu 1398

quite some are repeating multiple times