Linux - net.ipv4.conf.all

Question

I'm changing the default setting for arp_ignore on an ubuntu 16.04 server, from it's default value 0 to 1.

My understanding of the /proc/sys/net/ipv4/conf/ directory is that files under all will affect all interfaces, and default will affect newly created interfaces.

After changing the value of /proc/sys/net/ipv4/conf/all/arp_ignore to 1, the other files are still set to 0:

cat /proc/sys/net/ipv4/conf/*/arp_ignore
1
0
0
0

Does the value of /proc/sys/net/ipv4/conf/all/arp_ignore just override the interface specific files rather than changing their values?

score 1 · Accepted Answer · answered Jun 07 '18 at 13:36

I found some stuff here

    As far as I researched for IPv4 some time ago, the "default" value gets
copied to newly created interfaces only once.
"all" on the other hand allways gets applied in addition to the current
setting, but it depends on the exact setting, if its ORed, ANDed, or
whatevered:
    log_martians         OR
    accept_redirects     AND
    forwarding           ?
    mc_forwarding        AND
    medium_id
    proxy_arp            OR
    shared_media         OR
    secure_redirects     OR
    send_redirects       OR
    bootp_relay          AND
    accept_source_route  AND
    rp_filter            AND
    arp_filter           OR
    arp_announce         MAX
    arp_ignore           MAX
    arp_accept
    app_solicit
    disable_policy
    disable_xfrm
    tag
(see include/linux/inetdevice.h:83 for IN_DEV_{AND,OR,MAX}CONF)

Putting a new value in "all" doesn't change the value you read from
"$interface", but it only gets computed and used internally.

Linux - net.ipv4.conf.all

1 Answers1