EIGRP Prefix Limit

雪餅 福寿
イメージ、AS番号を分けたりしているわけではない

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, GigabitEthernet0/0
R9#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, GigabitEthernet0/0
R5#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, Tunnel0

After1(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       73

Restart-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 adjacency

iosv-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, GigabitEthernet0/0

clear 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。

Chapter: EIGRP MIB

参考

Chapter: EIGRP Prefix Limit Support


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