doc: Add documentation for AIGP

bgp bestpath aigp
neighbor PEER aigp

route-map X permit 10
 set aigp-metric <igp-metric|VALUE>

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

doc/user/bgp.rst

@@ -148,6 +148,12 @@ bottom until one of the factors can be used.
 
    Prefer higher local preference routes to lower.
 
+   If ``bgp bestpath aigp`` is enabled, and both paths that are compared have
+   AIGP attribute, BGP uses AIGP tie-breaking unless both of the paths have the
+   AIGP metric attribute. This means that the AIGP attribute is not evaluated
+   during the best path selection process between two paths when one path does
+   not have the AIGP attribute.
+
 3. **Local route check**
 
    Prefer local routes (statics, aggregates, redistributed) to received routes.
@@ -401,6 +407,17 @@ Route Selection
    paths learned from any of eBGP, iBGP, or confederation neighbors will
    be multipath if they are otherwise considered equal cost.
 
+.. clicmd:: bgp bestpath aigp
+
+   Use the bgp bestpath aigp command to evaluate the AIGP attribute during
+   the best path selection process between two paths that have the AIGP
+   attribute.
+
+   When bgp bestpath aigp is disabled, BGP does not use AIGP tie-breaking
+   rules unless paths have the AIGP attribute.
+
+   Disabled by default.
+
 .. clicmd:: maximum-paths (1-128)
 
    Sets the maximum-paths value used for ecmp calculations for this

doc/user/routemap.rst

@@ -310,6 +310,11 @@ Route Map Set Command
    trip time or `+rtt`/`-rtt` to add/subtract the round trip time to/from the
    MED.
 
+.. clicmd:: set aigp-metric <igp-metric|(1-4294967295)>
+
+   Set the BGP attribute AIGP to a specific value. If ``igp-metric`` is specified,
+   then the value is taken from the IGP protocol, otherwise an arbitrary value.
+
 .. clicmd:: set as-path prepend AS_PATH
 
    Set the BGP AS path to prepend.