Feral Packet

Protocol Priorities

Generally, but not always:

– Layer 2

-> Lower is better
-> PAgP port priority, higher is better

– IGPs and layer 3

-> Higher is better
-> OSPF has an exception

– BGP

-> There is a high / low cutoff

– Multicast

-> If the protocol has “Router” in the name, then higher is better
-> Think “Router” -> “IGP”
-> Otherwise, lower is better

Spanning-tree Protocol (STP):

– Root Bridge

-> Lowest bridge ID

-> Switch priority and MAC address

-> Lowest priority selected
-> Default is 32768
-> Range (increments of 4096) 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248, 57344, and 61440

-> SW1(config)#spanning-tree vlan 1-4094 root primary
-> SW1(config)#spanning-tree vlan 1-4094 root secondary
-> SW1(config)#spanning-tree vlan 1-4094 priority 4096
-> SW1(config)#spanning-tree mst 1 root primary
-> SW1(config)#spanning-tree mst 1 root secondary
-> SW1(config)#spanning-tree mst 1 priority 4096

-> Lowest base MAC address

– Root Port

-> Lowest root bridge ID
-> Lowest cost path to the root bridge
-> Default

-> 1000 Mb/s: 4
-> 100 Mb/s: 19
-> 10 Mb/s: 100

-> Range 1 to 200000000

-> SW1(config-if)#spanning-tree cost 3
-> SW1(config-if)#spanning-tree vlan 1-4094 cost 3
-> SW1(config-if)#spanning-tree mst 1 cost 3

-> Lowest designated bridge ID
-> Lowest designated path cost
-> Lowest received physical port number or port-id
-> Default is 128
-> Range (increments of 16) 0, 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, and 240.
-> Which is in the format of “.”

-> SW1(config-if)#spanning-tree port-priority 112
-> SW1(config-if)#spanning-tree vlan 1-4094 port-priority 112
-> SW1(config-if)#spanning-tree mst 1 port-priority 112

– Designated Port

-> Assigned to the port of the switch on the segment with the:

-> Lowest cost path to the root bridge
-> Lowest neighbor bridge ID
-> Lowest received port-priority

Link Aggregation Control Protocol (LACP):

– Master / Slave System Priority

-> Lowest system priority selected
-> Default is 32768
-> Range is 0 – 65535

-> SW1(config)#lacp system-priority 32767

-> Lowest MAC address
-> Lowest Port-ID

– Port Priority

-> Lowest priority selected
-> Default is 32768
-> Range is 0 – 65535

-> SW1(config-if)#lacp port-priority 32767

Port Aggregation Protocol (PAgP):

– Port Priority

-> Highest priority selected
-> Default is 128
-> Range 0 to 255

-> SW1(config-if)#pagp port-priority 129

Hot Standby Router Protocol (HSRP):

– Highest priority selected
– Default is 100
– Range is 0 to 255

-> SW1(config-if)#standby 1 priority 101

Virtual Router Redundancy Protocol (VRRP):

– Highest priority selected
– Default is 100
– Range is 1 to 254

-> SW1(config-if)#vrrp 1 priority 101

Gateway Load Balancing Protocol (GLBP):

– Highest priority selected
– Default is 100
– Range is 1 to 255

-> SW1(config-if)#glbp 1 priority 101

Intermediate System to Intermediate System (IS-IS):

– Designated Intermediate System (DIS)

-> Highest priority selected
-> Default is 64
-> Range 0 – 127

-> R1(config-if)#isis priority 65
-> R1(config-if)#isis priority 65 level-1
-> R1(config-if)#isis priority 65 level-2

Open Shortest Path First (OSPF):

– Designated Router (DR) / Backup Designated Router (BDR) Election

-> Highest priority selected
-> Default is 1
-> Range 0 – 255

-> R1(config-if)#ip ospf priority 2
-> R1(config-if)#ipv6 ospf neighbor 12::2 priority 2

– EXSTART Master / Slave Election

-> Higher router-id selected
-> R1(config-router)#router-id 0.0.0.2

– Forwarding Address

-> Lowest IP address
-> When dealing with LSA Type 4 and there are multiple paths

-> Broadcast network

Border Gateway Protocol (BGP):

– Weight

-> Higher value selected
-> Default is 0 for received routes
-> Default is 32768 for locally generated routes

-> R1(config)#route-map WEIGHT permit 10
-> R1(config-route-map)#set weight 1
-> R1(config-router)#neighbor 1.1.1.1 route-map WEIGHT in
-> R1(config-router)#neighbor 1.1.1.1 default-originate route-map WEIGHT in
-> R1(config)#route-map WEIGHT_LOCAL permit 10
-> R1(config-route-map)#set weight 32769
-> R1(config-router)#network 1.1.1.0 mask 255.255.255.0 route-map WEIGHT_LOCAL

– Local Preference

-> Higher value selected
-> Default is 100
-> Range 0 – 4294967295

-> R1(config-router)#bgp default local-preference 101
-> R1(config)#route-map LP permit 10
-> R1(config-route-map)#set local-preference 101
-> R1(config-router)#neighbor 1.1.1.1 route-map LP in
-> R1(config-router)#neighbor 1.1.1.1 default-originate route-map LP in
-> R1(config-router)#redistribute eigrp 1 route-map LP
-> R1(config-router)#redistribute ospf 1 route-map LP match internal external 1 external 2
-> R1(config-router)#network 1.1.1.0 mask 255.255.255.0 route-map LP
-> R1(config-router)#aggregate-address 1.1.2.0 255.255.255.252 attribute-map LP

* * * * High / Low (or shortest) Cutoff * * * *

– AS-PATH

-> Lowest number of organizations traversed is better
-> Shortest

-> R1(config)#route-map PREPEND permit 10
-> R1(config-route-map)#set as-path prepend 100 100
-> R1(config-router)#neighbor 1.1.1.1 route-map PREPEND out

– ORIGIN

-> Lowest type

– Multi-Exit Discriminator (MED)

-> Lowest value selected
-> Default is 0 for received routes
-> Default is IGP metric for locally generated routes (network or redistribute commands)
-> Range 0 to 65535

-> R1(config)#route-map MED permit 10
-> R1(config-route-map)#set metric 1
-> R1(config-router)#neighbor 1.1.1.1 route-map MED out
-> R1(config-router)#neighbor 1.1.1.1 default-originate route-map MED out
-> R1(config-router)#redistribute eigrp 1 metric 100
-> R1(config-router)#redistribute ospf 1 metric 100 match internal external 1 external 2
-> R1(config-router)#redistribute eigrp 1 route-map MED
-> R1(config-router)#redistribute ospf 1 route-map MED match internal external 1 external 2
-> R1(config-router)#network 1.1.1.0 mask 255.255.255.0 route-map MED
-> R1(config-router)#aggregate-address 1.1.2.0 255.255.255.252 attribute-map MED

– IGP Metric

-> Lowest

– Extended Community Cost

-> Lowest extended cost community is selected
-> IGP point of insertion (default)
-> Default is 2147483647
-> Range 0 and 4294967295

-> R1(config)#route-map EXTCOMMUMITYCOST permit 10</em>
-> R1(config-route-map)#set extcommunity cost 1 1
-> R1(config)#route-map EXTCOMMUMITYCOST permit 10
-> R1(config-route-map)#set extcommunity cost igp 1 1
-> R1(config-router)#neighbor 1.1.1.1 route-map EXTCOMMUMITYCOST out
-> R1(config-router)#neighbor 1.1.1.1 default-originate route-map EXTCOMMUMITYCOST out
-> R1(config-router)#redistribute eigrp 1 route-map EXTCOMMUMITYCOST
-> R1(config-router)#redistribute ospf 1 route-map EXTCOMMUMITYCOST match internal external 1 external 2
-> R1(config-router)#network 1.1.1.0 mask 255.255.255.0 route-map EXTCOMMUMITYCOST
-> R1(config-router)#aggregate-address 1.1.2.0 255.255.255.252 attribute-map EXTCOMMUMITYCOST

– Multipath External Paths

-> Path that was received first

– Cluster Length

-> Shortest

– Router-id

-> Lowest

– Neighbor Address

-> Lowest

– Extended Community Cost, pre-best path

-> Lowest extended community cost is selected
-> Pre-best path point on insertion
-> Default is 2147483647
-> Range 0 and 4294967295

-> R1(config)#route-map EXTCOMMCOST_PRE permit 10
-> R1(config-route-map)#set extcommunity cost pre-bestpath 1 1
-> R1(config-router)#neighbor 1.1.1.1 route-map EXTCOMMCOST_PRE out
-> R1(config-router)#neighbor 1.1.1.1 default-originate route-map EXTCOMMCOST_PRE out
-> R1(config-router)#redistribute eigrp 1 route-map EXTCOMMCOST_PRE
-> R1(config-router)#redistribute ospf 1 route-map EXTCOMMCOST_PRE match internal external 1 external 2
-> R1(config-router)#network 1.1.1.0 mask 255.255.255.0 route-map EXTCOMMCOST_PRE
-> R1(config-router)#aggregate-address 1.1.2.0 255.255.255.252 attribute-map EXTCOMMCOST_PRE