diff --git a/doc/user/zebra.rst b/doc/user/zebra.rst index 50c518d456..d54ca2a81e 100644 --- a/doc/user/zebra.rst +++ b/doc/user/zebra.rst @@ -292,6 +292,62 @@ Link Parameters Commands .. _zebra-vrf: +Administrative Distance +======================= + +Administrative distance allows FRR to make decisions about what routes +should be installed in the rib based upon the originating protocol. +The lowest Admin Distance is the route selected. This is purely a +subjective decision about ordering and care has been taken to choose +the same distances that other routing suites have choosen. + ++------------+-----------+ +| Protocol | Distance | ++------------+-----------+ +| System | 0 | ++------------+-----------+ +| Kernel | 0 | ++------------+-----------+ +| Connect | 0 | ++------------+-----------+ +| Static | 1 | ++------------+-----------+ +| NHRP | 10 | ++------------+-----------+ +| EBGP | 20 | ++------------+-----------+ +| EIGRP | 90 | ++------------+-----------+ +| BABEL | 100 | ++------------+-----------+ +| OSPF | 110 | ++------------+-----------+ +| ISIS | 115 | ++------------+-----------+ +| OPENFABRIC | 115 | ++------------+-----------+ +| RIP | 120 | ++------------+-----------+ +| Table | 150 | ++------------+-----------+ +| SHARP | 150 | ++------------+-----------+ +| IBGP | 200 | ++------------+-----------+ +| PBR | 200 | ++------------+-----------+ + +An admin distance of 255 indicates to Zebra that the route should not be +installed into the Data Plane. Additionally routes with an admin distance +of 255 will not be redistributed. + +Zebra does treat Kernel routes as special case for the purposes of Admin +Distance. Upon learning about a route that is not originated by FRR +we read the metric value as a uint32_t. The top byte of the value +is interpreted as the Administrative Distance and the low three bytes +are read in as the metric. This special case is to facilitate VRF +default routes. + Virtual Routing and Forwarding ==============================