list all route tables

I need to know how to list the IDs of all route tables. For example, I can run:

ip rule add fwmark 2 table 104
ip route add dev eth0 default via 192.168.3.7 table 104

A call to ip rule list shows:

0:  from all lookup local 
32765:  from all fwmark 0x2 lookup 104 
32766:  from all lookup main 
32767:  from all lookup default

And a call to ip route show table 104 shows:

default via 192.168.3.7 dev eth0

If I then call ip rule del table 104, a subsequent call to ip rule list shows:

0:  from all lookup local 
32766:  from all lookup main 
32767:  from all lookup default

However, a call to ip route show table 104 still shows:

default via 192.168.3.7 dev eth0

I know that I can flush the table using ip route flush table 104. I'd like to be able to flush all tables that are not local, main, and default. Thus I want to be able to list the existing tables.

I've seen people use cat /etc/iproute2/rt_tables, but that only produces:

#
# reserved values
#
255 local
254 main
253 default
0   unspec
#
# local
#
#1  inr.ruhep

What can I do to get all the table names that currently exist? Thanks in advance!

Solution 1:

There exists a way to list all routing entries of all tables. ip route show table all

Using some shell piping magic, you can extract all table names and IDs like this:

ip route show table all | grep "table" | sed 's/.*\(table.*\)/\1/g' | awk '{print $2}' | sort | uniq

or

ip route show table all | grep -Po 'table \K[^\s]+' | sort -u

If you only care about the numeric table names, add some grep filtering:

ip route show table all | grep "table" | sed 's/.*\(table.*\)/\1/g' | awk '{print $2}' | sort | uniq | grep -e "[0-9]"

or

ip route show table all | grep -Po 'table \K[^\s]+' | sort -u | grep -e "[0-9]"

Solution 2:

What can I do to get all the table names that currently exist?

The file /etc/iproute2/rt_tables is the only source of table names on the system. Internally, routing tables have integer identifiers.

The rest of your question is a bit confusing. If a table is not referenced by a rule, then it is effectively "deleted" because it has no impact on the routing of the system. So you can list all the active routing tables like this:

ip rule list | awk '/lookup/ {print $NF}'

That looks for all lookup action in the routing rules and prints the target.

It looks like routing table are identified by a 64 bit integer. If you really, really wanted to find all routing tables with rules, even the inactive ones that have no impact on your system, you could simple iterate a loop from 1 to 2^64:

seq 0 $(echo '2 64 ^ p' | dc) | xargs -iTABLE sh -c 'echo === TABLE ===; ip route show table TABLE'

...but this will take forever and ever, because 64 bits covers a lot of space.

Solution 3:

(egrep '^\s*[0-9]' /etc/iproute2/rt_tables | awk '{print $2}' | sort -u; ip rule list | awk '/lookup/ {print $NF}' | sort -u; ip route show table all | sed 's/.*\(table.*\)/\1/g' | awk '{if($0 ~ /table/) print $2; else print "main";}' | sort -u) | sort | uniq -c

Gratitude for this thread leading to this combo that shows all the routing tables that currently contain routes, that are referenced by rules, and that are named, with a 3 next to each table that has content, is referenced, and is named or a 2 or a 1 if one or two of the three conditions apply.