EIGRP Prefix Limit
設定
iosv-3からiosv-7へiosv-1-5をEIGRPで広告。
Before
R7#sh ip ro eigrp | b Gate
Gateway of last resort is not set
155.1.0.0/16 is variably subnetted, 11 subnets, 2 masks
D 155.1.0.0/24
[90/76805120] via 155.1.37.3, 00:07:44, GigabitEthernet0/0
D 155.1.13.0/24 [90/15360] via 155.1.37.3, 00:07:44, GigabitEthernet0/0
D 155.1.23.0/24 [90/15360] via 155.1.37.3, 00:07:44, GigabitEthernet0/0R9#sh ip ro eigrp | b Gate
Gateway of last resort is not set
155.1.0.0/16 is variably subnetted, 9 subnets, 2 masks
D 155.1.0.0/24
[90/76810240] via 155.1.79.7, 00:12:18, GigabitEthernet0/0
D 155.1.13.0/24 [90/20480] via 155.1.79.7, 00:12:19, GigabitEthernet0/0
D 155.1.23.0/24 [90/20480] via 155.1.79.7, 00:12:18, GigabitEthernet0/0
D 155.1.37.0/24 [90/15360] via 155.1.79.7, 00:27:11, GigabitEthernet0/0
D 155.1.67.0/24 [90/15360] via 155.1.79.7, 00:27:11, GigabitEthernet0/0R5#sh ip ro eigrp | b Gate
Gateway of last resort is not set
155.1.0.0/16 is variably subnetted, 13 subnets, 2 masks
D 155.1.13.0/24 [90/25856256] via 155.1.0.3, 00:11:36, Tunnel0
D 155.1.23.0/24 [90/25856256] via 155.1.0.3, 00:11:36, Tunnel0
D 155.1.37.0/24 [90/25856256] via 155.1.0.3, 00:11:36, Tunnel0
D 155.1.67.0/24 [90/25856512] via 155.1.0.3, 00:11:36, Tunnel0
D 155.1.79.0/24 [90/25856512] via 155.1.0.3, 00:11:36, Tunnel0After1(単一ネイバー)
maximum-prefix 2を設定
R3(config-router-af)#neighbor 155.1.37.7 maximum-prefix 2
R3(config-router-af)#
%DUAL-3-PFXLIMIT: EIGRP-IPv4 100: Neighbor prefix limit reached(2).
R3(config-router-af)#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.7 (GigabitEthernet0/3) is down: prefix-limit exceeded
R7#sh ip ro eigrp | b Gate
Gateway of last resort is not set
R7#sh ip eigrp neighbor
EIGRP-IPv4 VR(cisco) Address-Family Neighbors for AS(100)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 155.1.37.3 Gi0/0 11 00:01:08 1 5000 1 0
2 155.1.79.9 Gi0/2 14 00:32:18 8 100 0 10
1 155.1.67.6 Gi0/1 14 00:32:18 7 100 0 10ネイバーは継続するものの、iosv-3から経路は広告されない。
R9#sh ip ro eigrp | b Gate
Gateway of last resort is not set
155.1.0.0/16 is variably subnetted, 6 subnets, 2 masks
D 155.1.37.0/24 [90/15360] via 155.1.79.7, 00:34:11, GigabitEthernet0/0
D 155.1.67.0/24 [90/15360] via 155.1.79.7, 00:34:11, GigabitEthernet0/0また、neighbor maximum-prefixで指定されたのはiosv-7だけど、その先にあるiosv-9にまで影響が及んでいる（iosv-7がiosv-3から広告されていないのでiosv-9も経路を学習できない。）
R5#sh ip ro eigrp | b Gate
Gateway of last resort is not set
155.1.0.0/16 is variably subnetted, 11 subnets, 2 masks
D 155.1.13.0/24 [90/25856256] via 155.1.0.3, 00:19:17, Tunnel0
D 155.1.23.0/24 [90/25856256] via 155.1.0.3, 00:19:17, Tunnel0
D 155.1.37.0/24 [90/25856256] via 155.1.0.3, 00:19:17, Tunnel0さらにiosv-3視点でiosv-7の反対側にあるiosv-5ではiosv-7の持つ経路を学習していない。（iosv-3の持つ経路は通常通り広告されている）
show eigrp add ipv4 accounting
R3(config-router-af)#do sh eigrp add ipv4 accounting
EIGRP-IPv4 VR(cisco) Accounting for AS(100)/ID(150.1.3.3)
Total Prefix Count: 4 States: A-Adjacency, P-Pending, D-Down
State Address/Source Interface Prefix Restart Restart/
Count Count Reset(s)
A 155.1.13.1 Gi0/1 0 0 0
A 155.1.0.5 Tu0 0 0 0
A 155.1.23.2 Gi0/2 0 0 0
P 155.1.37.7 Gi0/3 0 2 73Restart-time中にprefix超過が改善されないためリセットされまくってる。また、Restartのデフォルトは5分なので最初に超過があってから約10分程度経ったことがわかる。
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is up: new adjacency
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is down: retry limit exceeded
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is up: new adjacency
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is down: retry limit exceeded
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is up: new adjacency
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is down: retry limit exceeded
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is up: new adjacencyiosv-7ではup/downを繰り返している。
warning-only
R3(config-router-af)#neighbor 155.1.37.7 maximum-prefix 2 warning-only
R3(config-router-af)#do sh run | s eigrp
router eigrp cisco
!
address-family ipv4 unicast autonomous-system 100
!
topology base
exit-af-topology
neighbor 155.1.37.7 maximum-prefix 2 warning-only
network 155.1.0.0 0.0.0.255
network 155.1.13.0 0.0.0.255
network 155.1.23.0 0.0.0.255
network 155.1.37.0 0.0.0.255
exit-address-family
R3(config-router-af)#do clear ip eigrp neighbor 155.1.37.3
R7#clear ip eigrp neighbor 155.1.37.3
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is down: manually cleared
R7#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.3 (GigabitEthernet0/0) is up: new adjacency
R7#sh ip ro eigrp | b Gate
Gateway of last resort is not set
R3(config-router-af)#do sh eigrp add ipv4 accounting
EIGRP-IPv4 VR(cisco) Accounting for AS(100)/ID(150.1.3.3)
Total Prefix Count: 4 States: A-Adjacency, P-Pending, D-Down
State Address/Source Interface Prefix Restart Restart/
Count Count Reset(s)
A 155.1.13.1 Gi0/1 0 0 0
A 155.1.0.5 Tu0 0 0 0
A 155.1.23.2 Gi0/2 0 0 0
D 155.1.37.7 Gi0/3 0 3 0既にprefix超過しているiosv-7に向けてwarning-onlyを上書きするもDownしたまま。clear ip eigrp neighborを入れてもなしのつぶて。
clear eigrp add ipv4 neighbor
R3(config-router-af)#do clear eigrp add ipv4 neighbor 155.1.37.7
R3(config-router-af)#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.7 (GigabitEthernet0/3) is up: new adjacency
R3(config-router-af)#
%DUAL-4-PFXLIMITTHR: EIGRP-IPv4 100: Neighbor threshold prefix level(1) reached.
R3(config-router-af)#
%DUAL-3-PFXLIMIT: EIGRP-IPv4 100: Neighbor prefix limit reached(2).
R3(config-router-af)#do sh eigrp add ipv4 accounting
EIGRP-IPv4 VR(cisco) Accounting for AS(100)/ID(150.1.3.3)
Total Prefix Count: 6 States: A-Adjacency, P-Pending, D-Down
State Address/Source Interface Prefix Restart Restart/
Count Count Reset(s)
A 155.1.37.7 Gi0/3 2 0 0
A 155.1.13.1 Gi0/1 0 0 0
A 155.1.0.5 Tu0 0 0 0
A 155.1.23.2 Gi0/2 0 0 0
R7#sh ip ro eigrp | b Gate
Gateway of last resort is not set
155.1.0.0/16 is variably subnetted, 11 subnets, 2 masks
D 155.1.0.0/24
[90/76805120] via 155.1.37.3, 00:00:23, GigabitEthernet0/0
D 155.1.13.0/24 [90/15360] via 155.1.37.3, 00:00:23, GigabitEthernet0/0
D 155.1.23.0/24 [90/15360] via 155.1.37.3, 00:00:23, GigabitEthernet0/0clear eigrp add ipv4 neighborを入れる必要があったみたい。ただ、CCOではclear ip eigrp neighborでもいけるみたいなことが書かれてある。おそらく、address-family内でnetworkコマンドを入力しているからだと思う。
After2(全ネイバー)
R3(config-router-af)#maximum-prefix 2
R3(config-router-af)#
%DUAL-3-PFXLIMIT: EIGRP-IPv4 100: Aggregate prefix limit reached(2).
R3(config-router-af)#
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.37.7 (GigabitEthernet0/3) is down: prefix-limit exceeded
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.0.5 (Tunnel0) is down: prefix-limit exceeded
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.23.2 (GigabitEthernet0/2) is down: prefix-limit exceeded
%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 155.1.13.1 (GigabitEthernet0/1) is down: prefix-limit exceeded
R7#sh ip ro eigrp | b Gate
Gateway of last resort is not set
R5#sh ip ro eigrp | b Gate
Gateway of last resort is not set当然、iosv-3の全ネイバーがPendingになる。
R3(config-router-af)#do sh eigrp add ipv4 accounting
EIGRP-IPv4 VR(cisco) Accounting for AS(100)/ID(150.1.3.3)
Total Prefix Count: 4 States: A-Adjacency, P-Pending, D-Down
State Address/Source Interface Prefix Restart Restart/
Count Count Reset(s)
P Redistributed ---- 0 1 184
P 155.1.13.1 Gi0/1 0 1 184
P 155.1.23.2 Gi0/2 0 1 184
P 155.1.0.5 Tu0 0 1 184
P 155.1.37.7 Gi0/3 0 1 184
超豆知識
このPrefix Limit機能だけ、EIGRPのSNMPトラップに対応していない。
この知識が役に立つことは０だと思う。
参考
Chapter: EIGRP Prefix Limit Support