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
 ==============================
 
diff --git a/tests/topotests/all-protocol-startup/r1/ipv4_routes.ref b/tests/topotests/all-protocol-startup/r1/ipv4_routes.ref
index 0a20231371..a7d6fe11a6 100644
--- a/tests/topotests/all-protocol-startup/r1/ipv4_routes.ref
+++ b/tests/topotests/all-protocol-startup/r1/ipv4_routes.ref
@@ -15,6 +15,7 @@ S>* 4.5.6.11/32 [1/0] via 192.168.0.2, r1-eth0, XX:XX:XX
 S>* 4.5.6.12/32 [1/0] is directly connected, r1-eth0, XX:XX:XX
 S>* 4.5.6.13/32 [1/0] unreachable (blackhole), XX:XX:XX
 S>* 4.5.6.14/32 [1/0] unreachable (blackhole), XX:XX:XX
+S   4.5.6.15/32 [255/0] via 192.168.0.2, r1-eth0, XX:XX:XX
 S>* 4.5.6.7/32 [1/0] unreachable (blackhole), XX:XX:XX
 S>* 4.5.6.8/32 [1/0] unreachable (blackhole), XX:XX:XX
 S>* 4.5.6.9/32 [1/0] unreachable (ICMP unreachable), XX:XX:XX
diff --git a/tests/topotests/all-protocol-startup/r1/ipv6_routes.ref b/tests/topotests/all-protocol-startup/r1/ipv6_routes.ref
index 6e3e9c87c1..d5bc16a2bf 100644
--- a/tests/topotests/all-protocol-startup/r1/ipv6_routes.ref
+++ b/tests/topotests/all-protocol-startup/r1/ipv6_routes.ref
@@ -20,9 +20,10 @@ C * fe80::/64 is directly connected, r1-eth7, XX:XX:XX
 C * fe80::/64 is directly connected, r1-eth8, XX:XX:XX
 C * fe80::/64 is directly connected, r1-eth9, XX:XX:XX
 O   fc00:0:0:4::/64 [110/10] is directly connected, r1-eth4, XX:XX:XX
-S>* 4:5::/32 [1/0] is directly connected, r1-eth0, XX:XX:XX
 S>* 4:5::6:10/128 [1/0] via fc00::2, r1-eth0, XX:XX:XX
 S>* 4:5::6:11/128 [1/0] via fc00::2, r1-eth0, XX:XX:XX
+S>* 4:5::6:12/128 [1/0] is directly connected, r1-eth0, XX:XX:XX
+S   4:5::6:15/128 [255/0] via fc00::2, r1-eth0, XX:XX:XX
 S>* 4:5::6:7/128 [1/0] unreachable (blackhole), XX:XX:XX
 S>* 4:5::6:8/128 [1/0] unreachable (blackhole), XX:XX:XX
 S>* 4:5::6:9/128 [1/0] unreachable (ICMP unreachable), XX:XX:XX
diff --git a/tests/topotests/all-protocol-startup/r1/zebra.conf b/tests/topotests/all-protocol-startup/r1/zebra.conf
index c621593ef7..85c8676964 100644
--- a/tests/topotests/all-protocol-startup/r1/zebra.conf
+++ b/tests/topotests/all-protocol-startup/r1/zebra.conf
@@ -20,7 +20,12 @@ ip route 4.5.6.11/32 192.168.0.2 r1-eth0
 ipv6 route 4:5::6:11/128 fc00:0:0:0::2 r1-eth0
 # Create ifname routes
 ip route 4.5.6.12/32 r1-eth0
-ipv6 route 4:5::6:12/32 r1-eth0
+ipv6 route 4:5::6:12/128 r1-eth0
+# Create a route that has a large admin distance
+# an admin distance of 255 should be accepted
+# by zebra but not installed.
+ip route 4.5.6.15/32 192.168.0.2 255
+ipv6 route 4:5::6:15/128 fc00:0:0:0::2 255
 !
 interface r1-eth0
  description to sw0 - no routing protocol