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zebra: Add some flavor documentation for ECMP in zebra

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Signed-off-by: Donald Sharp <sharpd@nvidia.com>
This commit is contained in:
Donald Sharp 2021-04-20 09:03:00 -04:00
parent 85e40093a9
commit df55b448e9
1 changed files with 72 additions and 0 deletions
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doc/user/zebra.rst
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@ -463,6 +463,78 @@ be updated with the new name. To illustrate, if you want to recompile with
./configure --with-defaultvrfname=global ./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: .. _zebra-mpls:
MPLS Commands MPLS Commands