mjhjmtu

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?

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,MAXCONF)

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