Linux 3.6 removed the ipv4 routing cache (commit).
Remove the ipv4 routing cache. Now lookups go directly into the FIB trie and use prebuilt routes cached there.
According to this question, the routing cache entries are now stored in a "routing exception" structure which is a part of the routing entry.
On my 3.16 (Debian Jessie) standard distribution kernel, I can't see any exceptions and
ip route show cache doesn't return anything.
The routing table only has a default route:
~#ip route show
default via 10.11.2.30 dev eth0
10.11.0.0/16 dev eth0 proto kernel scope link src 10.11.1.76
Q1: How can I list all of these routing exceptions that are known to the kernel?
Q2: How can I selectively remove such an exception?
Q3: Why does the kernel not select the correct default gateway when trying to ping a certain host:
PING 10.30.104.23 (10.30.104.23) 56(84) bytes of data.
From 10.11.1.11 icmp_seq=1 Destination Protocol Unreachable
Addition for Q3: I suspect that this (now obsolete) route was probably stored (somewhere) because of a ICMP redirect. But if
ip route show cache does not list routing exceptions and the default route says otherwise - where is this bit of information stored?