From: Donald Sharp Date: Tue, 20 Apr 2021 13:03:00 +0000 (-0400) Subject: zebra: Add some flavor documentation for ECMP in zebra X-Git-Tag: base_8.0~104^2 X-Git-Url: https://git.puffer.fish/?a=commitdiff_plain;h=refs%2Fpull%2F8520%2Fhead;p=mirror%2Ffrr.git zebra: Add some flavor documentation for ECMP in zebra Signed-off-by: Donald Sharp --- diff --git a/doc/user/zebra.rst b/doc/user/zebra.rst index 205b25e53e..6d4e488fdb 100644 --- a/doc/user/zebra.rst +++ b/doc/user/zebra.rst @@ -463,6 +463,78 @@ be updated with the new name. To illustrate, if you want to recompile with ./configure --with-defaultvrfname=global +.. _zebra-ecmp: + +ECMP +==== + +FRR supports ECMP as part of normal operations and is generally compiled +with a limit of 64 way ECMP. This of course can be modified via configure +options on compilation if the end operator desires to do so. Individual +protocols each have their own way of dictating ECMP policy and their +respective documentation should be read. + +ECMP can be inspected in zebra by doing a `show ip route X` command. + +.. code-block:: shell + + eva# show ip route 4.4.4.4/32 + Codes: K - kernel route, C - connected, S - static, R - RIP, + O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP, + T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP, + F - PBR, f - OpenFabric, + > - selected route, * - FIB route, q - queued, r - rejected, b - backup + t - trapped, o - offload failure + + D>* 4.4.4.4/32 [150/0] via 192.168.161.1, enp39s0, weight 1, 00:00:02 + * via 192.168.161.2, enp39s0, weight 1, 00:00:02 + * via 192.168.161.3, enp39s0, weight 1, 00:00:02 + * via 192.168.161.4, enp39s0, weight 1, 00:00:02 + * via 192.168.161.5, enp39s0, weight 1, 00:00:02 + * via 192.168.161.6, enp39s0, weight 1, 00:00:02 + * via 192.168.161.7, enp39s0, weight 1, 00:00:02 + * via 192.168.161.8, enp39s0, weight 1, 00:00:02 + * via 192.168.161.9, enp39s0, weight 1, 00:00:02 + * via 192.168.161.10, enp39s0, weight 1, 00:00:02 + * via 192.168.161.11, enp39s0, weight 1, 00:00:02 + * via 192.168.161.12, enp39s0, weight 1, 00:00:02 + * via 192.168.161.13, enp39s0, weight 1, 00:00:02 + * via 192.168.161.14, enp39s0, weight 1, 00:00:02 + * via 192.168.161.15, enp39s0, weight 1, 00:00:02 + * via 192.168.161.16, enp39s0, weight 1, 00:00:02 + +In this example we have 16 way ecmp for the 4.4.4.4/32 route. The `*` character +tells us that the route is installed in the Data Plane, or FIB. + +If you are using the Linux kernel as a Data Plane, this can be inspected +via a `ip route show X` command: + +.. code-block:: shell + + sharpd@eva ~/f/doc(ecmp_doc_change)> ip route show 4.4.4.4/32 + 4.4.4.4 nhid 185483868 proto sharp metric 20 + nexthop via 192.168.161.1 dev enp39s0 weight 1 + nexthop via 192.168.161.10 dev enp39s0 weight 1 + nexthop via 192.168.161.11 dev enp39s0 weight 1 + nexthop via 192.168.161.12 dev enp39s0 weight 1 + nexthop via 192.168.161.13 dev enp39s0 weight 1 + nexthop via 192.168.161.14 dev enp39s0 weight 1 + nexthop via 192.168.161.15 dev enp39s0 weight 1 + nexthop via 192.168.161.16 dev enp39s0 weight 1 + nexthop via 192.168.161.2 dev enp39s0 weight 1 + nexthop via 192.168.161.3 dev enp39s0 weight 1 + nexthop via 192.168.161.4 dev enp39s0 weight 1 + nexthop via 192.168.161.5 dev enp39s0 weight 1 + nexthop via 192.168.161.6 dev enp39s0 weight 1 + nexthop via 192.168.161.7 dev enp39s0 weight 1 + nexthop via 192.168.161.8 dev enp39s0 weight 1 + nexthop via 192.168.161.9 dev enp39s0 weight 1 + +Once installed into the FIB, FRR currently has little control over what +nexthops are choosen to forward packets on. Currently the Linux kernel +has a `fib_multipath_hash_policy` sysctl which dictates how the hashing +algorithm is used to forward packets. + .. _zebra-mpls: MPLS Commands