Arista EOS PBR (1)

• PBR = Policy Based Routing - 就是不走IP routing path，而是policy defined path
• Arista EOS PBR configuration和Cisco有点不一样, Arista允许 Raw match
• Cisco:
• access-list 1 perm ip 1.1.1.0 0.0.0.255
• route-map pbrRtmap perm 10
• match ip address 1
• set ip next-hop 2.2.2.2
• Arista:
• policy-map type pbr pbrPolicy
• 10 match ip 1.1.1.0/24 any set nexthop recursive 2.2.2.2
• Sand Platform实施有点特别：
• 如果是routed/LAG上面配置, 只要一个set of TCAM，而且只在Faps that host this routed/LAG ports. 和Port ACL类似
• 如果是VLAN/SVI上配置，每个SVI都有一个copy of TACM rules，而且是在所有Faps。
• 所以routed/LAG scale更好
• set nexthop recursive是为了ECMP
• 如果no set = no action = bypass pbr and move to next stage. 
• 如果不satisfy 如何match，就去routing
• 如果NH不能Resolved, 直接drop
• 知道via = vlan, eth and MAC
• Configuration:
• class-map type pbr match-any pbrClassMap
• 10 match ip access pbrACL1
• policy-map type pbr pbrPolicy
• 10 class pbrClassMap
• set next-hop ip-address <ip1> <ip2>....
• interface e1
• service-policy type pbr input pbrPolicy 
• 如果policy-map applied to a Lag，但是Lag member port有policy-map，咋办？
• member port's policy-map就作废了
• ECMP support for PBR
• set next-hop ip-addr nh1 nh2... nhN
• N = max# of ECMP
• No UCMP, 如果是同样的Via, 会被filter out
• Reference:
• Cisco PBR white paper (cat6500)
• AD 1622/1206/1914