Big LAN and ARP broadcast
Sometimes the network suffers from a very BAD design (like large L2 domain).
In this situation, some (normal) network behavior are more visible than it should if the network had a better designer.
The reason of the bad design is often part of the history OR the hired consultant dislikes th company he works for and ship them with a bad design :D
One of the visible phenomenon occurs when many hosts are populated in ARP caches and the local table overflows. The default ARP cache on Linux (and every other OS) are not suited for the bad designed networks.
It results in broadcast storms that kills network performances. Another side effect that double the bad effect is when you have configured broadcast rate-limiter. This feature could kills ARP broadcast and make the packets dance … dance again and again through your L2 network.
To fix the network, you must go in two directions:
- re-think your broadcast rate-limiter (in some network devices it’s done automatically without configuration! don’t trust the vendor pre-sales in his well-suited costume, trust the packets!
- adjust ARP cache and garbage collector settings on your end hosts. And adjust CAM age entries on your transit L2 devices. For Linux, you can go with those parameters:
$ sudo echo ‘net.ipv4.neigh.default.gc_thresh3’ = 4096 » /etc/sysctl.conf
$ sudo echo ‘net.ipv4.neigh.default.gc_thresh2’ = 2048 » /etc/sysctl.conf
$ sudo echo ‘net.ipv4.neigh.default.gc_thresh1’ = 1024 » /etc/sysctl.conf
$ sudo sysctl -p
Et voilà!
23 Notes/ Hide
-
reintroduceb liked this
-
microprocess liked this
-
deafpant65 liked this
-
youngadultsextremelatex liked this
-
insertionshotsmother liked this
-
shadyevasion liked this
-
fropert posted this
pello lives near Paris (France)