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network plumber s journal skip to main skip to sidebar network plumber s journal linux networking and related topics monday september 24 2012 vxlan for linux vxlan for linux just published a linux kernel implementation of vxlan for possible inclusion in 3 7 kernel patches for those unfamiliar with vxlan here are some common questions q what is vxlan it is a standard protocol to transfer layer 2 ethernet packets over udp q what is the vxlan protocol the standard is under development the current draft rfc is at version 2 q why do we need yet another tunnel protocol why not just use gre existing tunnel protocols depend on properties of the backbone which may not be available generic routing encapsulation works by tunneling over ip and maybe blocked at routers by firewalls that only accept tcp and udp q does openvswitch already do vxlan the development version of openvswitch does have vxlan support but ovs is fundamentally different than normal linux networking many people may not want to take the jump into ovs there are many cases where existing linux networking technologies are easier to configure and use q what could vxlan in linux be used for it could be used to terminate vxlan in linux router or link linux bridges across hypervisors or talk to legacy expensive virtualization products q why is vxlan cool read the blogosphere here are some good starting points ivan pepelnjak vxlan and otv i ve been suckered digging deeper into vxlan part 1 examining vxlan nvgre vs vxlan on packetpushers podcast q that s too technical what can i show my manager there is a short introductory video on the fundamentals of vxlan posted by linux network plumber at 12 37 pm no comments email this blogthis share to x share to facebook share to pinterest labels networking vxlan monday february 28 2011 net snmp ip forward table performance problems some performance problems are hard and complex but others seem to be due to just plain stupidity this is the saga of snmp daemon and a full bgp route table way back in 2006 vyatta discovered that if an snmp walk was done on a server with a full bgp route table it would peg the cpu and never complete a full bgp route table is 500k entries or more so it does a good job of exposing scalability nightmares the initial fix was to disable the caching of the route table in snmp which made it return no entries hardly a good fix but returning nothing is better than crashing i began investigating with the simple tools of packet capture with wireshark and syscall capturing with strace the first discovery was that each request caused the tcp wrappers library to open and read etc hosts allow and etc hosts deny bogus on two counts debian is shipping the 2 files with no real entries only comments each packet caused file to be read but there was really no data it would have been better to have the file not exist and have the open fail but for our distribution there was no point in enabling tcp wrappers anyway the fix was simple to disable tcp wrappers the net snmp daemon retrieves the ipv4 and ipv6 routing table the old school way through proc this isn t a total disaster but since the route entries in proc start with an interface name and net snmp wants an ifindex it looks up each entry that is 300k extra ioctl calls short term hack was to just cache last ifname ifindex translation later i replaced it with a netlink route dump which gives ifindex surprisingly netlink route dump is already used in another mib next observation was that it is stupid to use snmpwalk to walk the whole system and instead use snmpbulk this helps but still the walk would not complete the real discovery was when looking at the net snmp container code internally net snmp uses an objectish abstraction to store data and the main ones are a flat table and a linked list the table is stored in sorted order for fast lookup and sequential access new entries are placed at the end of the table and a dirty bit is set for next lookup the problem is that each insert also does a lookup for duplicates which causes a sort this makes inserts do quicksort for each entry there is the scalability problem to make it more interesting net snmp creates the route table twice first it reads table from proc and puts entries in one table then walks that table to create the cache table used for lookup loading the cache with non scalable insertion takes several minutes on a really fast machine and the cache timeout is 30 seconds this ends up causing the cpu load because each request finds a dirty cache and does a full reload now for the good news fixing the insert wasn t the hard the first step was realizing that the temporary table doesn t have to a table container instead it can be changed to a fifo linked list the fifo container is o 1 on insert the actual cache container requires a different approach the table container has an unused flag to allow duplicates in the table turning the allow_duplicates flag makes inserts much faster because the table is not sorted until the first request these get the table load down to less than a 5 seconds on fast machine lastly a couple of other improvements help as well when the binary_table is expanded the code would calloc a new area copy the old data and then free the original this is much worse than just using realloc which can usually in place expansion when table is getting large the sort function can be optimized to avoid calling the comparison function and using a faster insertion sort for small sub sections these get the load down to less than a second extra credit to the first developer who implements a new net snmp container using something better for big tables like avl or b tree posted by linux network plumber at 12 45 pm 1 comment email this blogthis share to x share to facebook share to pinterest labels networking performance snmp thursday march 18 2010 gtsm i like seeing lwn writers pick up small patches and explain what they are why they are important as a developer often the impact of a change is not obvious and without further explanation significant changes go unnoticed the recent story about generalized ttl security measures in lwn net is one such example but when a story comes out the writer should do research on the background first it is nice to give some credit to the author and vyatta as well as also some history i did this patch based on an enhancement request for the current vyatta version the starting point was a unaccepted patch to quagga and existing implementation for freebsd systems it was one of those patches where the kernel change took less time than writing the test programs also the initial patch wasn t perfect since nothing ever is since it broke time wait sockets and missed the case of icmp messages both should be fixed by the time 2 6 34 rc2 comes out also the necessary support has not been integrated into upstream quagga yet i appreciate the review and feedback from eric andi david and pekka for making this work posted by linux network plumber at 10 53 pm 1 comment email this blogthis share to x share to facebook share to pinterest labels network tcp wednesday november 11 2009 powerpoint karoke contest anyone in the portland area interested in a fun and creative event is invited to the 1st timbertalkers powerpoint karoke contest on tuesday 11 24 at noon meeting location is 9403 b sw nimbus ave beaverton oregon if you have never done pptk here are the rules topic is draw from set of 30 topics probably 10 to 15 slides speaker will have 2 to 3 minutes prizes awarded in spirit of open source it will really be a openoffice impress contest and the slides will be drawn from creative commons licensed decks posted by linux network plumber at 4 43 pm no comments email this blogthis share to x share to facebook share to pinterest labels pptk toastmasters tuesday october 27 2009 ubuntu 9 10 hates kernel developers ubuntu has never been the easiest distribution to do kernel development but it looks like with 9 10 it has made things too painful i need to build and install kernels all the time and usually just update grub menu manually but now with grub 2 in ubuntu 9 10 they have wrapped the grub menu in grub mkconfig why it would be great if the system was setup so just doing make install in the kernel source put in the kernel and updated the grub cfg but no that would make too much sense p s they managed to break the sky2 driver somehow the connection won t come up and negotiates the wrong speed it turned out not to be a kernel problem wiring issue speed combined with some network manager changes posted by linux network plumber at 8 42 pm 5 comments email this blogthis share to x share to facebook share to pinterest tuesday october 20 2009 japan linux symposium i am giving three talks 1 routing performance 2 staging drivers 3 vyatta cli so if you are attending jls please stop by and give me support posted by linux network plumber at 1 25 am no comments email this blogthis share to x share to facebook share to pinterest thursday september 17 2009 netconf linuxcon linux plumber s conference it will be a busy week the network developer s are getting together at netconf over the weekend then linuxcon followed by linux plumber s conference hope the weather holds out portland has a tendency to rain when ever there is a big event posted by linux network plumber at 9 20 am no comments email this blogthis share to x share to facebook share to pinterest labels conference network older posts home subscribe to posts atom blog archive 2012 1 september 1 vxlan for linux 2011 1 february 1 2010 1 march 1 2009 7 november 1 october 2 september 1 july 1 june 1 february 1 2008 8 december 1 october 1 september 1 august 2 june 2 january 1 2007 1 december 1 about me linux network plumber view my complete profile