4 バイト AS な BGP パケットをキャプチャしてみる
4 バイト AS 設定されたルータ間で BGP のパケットをキャプチャしてみました。
構成
以下の構成で検証しました。いずれも Cisco IOS 15.4(1)T を使っています。
全ルータで 4 バイト AS を設定します。R5 で Loopback0 に割り当てた「10.0.99.5/32」を BGP で広報します。それを R1 でパケットをキャプチャし「どのように見えるか？」を確認します。
コンフィグ
4 バイト AS の表記を「ドット区切り」にする為、bgp asnotation dot を設定しています。
R1 のコンフィグ
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16 | hostname R1
!
interface Loopback99
ip address 10.0.99.1 255.255.255.255
!
interface Ethernet0/0
ip address 10.0.12.1 255.255.255.0
no shutdown
!
router bgp 100.1
bgp router-id 10.0.99.1
bgp asnotation dot
bgp log-neighbor-changes
neighbor 10.0.12.2 remote-as 100.2
!
end
|
R2 のコンフィグ
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21 | hostname R2
!
interface Loopback99
ip address 10.0.99.2 255.255.255.255
!
interface Ethernet0/0
ip address 10.0.12.2 255.255.255.0
no shutdown
!
interface Ethernet0/1
ip address 10.0.23.2 255.255.255.0
no shutdown
!
router bgp 100.2
bgp router-id 10.0.99.2
bgp asnotation dot
bgp log-neighbor-changes
neighbor 10.0.12.1 remote-as 100.1
neighbor 10.0.23.3 remote-as 100.3
!
end
|
R3 のコンフィグ
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21 | hostname R3
!
interface Loopback99
ip address 10.0.99.3 255.255.255.255
!
interface Ethernet0/1
ip address 10.0.23.3 255.255.255.0
no shutdown
!
interface Ethernet0/2
ip address 10.0.34.3 255.255.255.0
no shutdown
!
router bgp 100.3
bgp router-id 10.0.99.3
bgp asnotation dot
bgp log-neighbor-changes
neighbor 10.0.23.2 remote-as 100.2
neighbor 10.0.34.4 remote-as 100.4
!
end
|
R4 のコンフィグ
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21 | hostname R4
!
interface Loopback99
ip address 10.0.99.4 255.255.255.255
!
interface Ethernet0/2
ip address 10.0.34.4 255.255.255.0
no shutdown
!
interface Ethernet0/3
ip address 10.0.45.4 255.255.255.0
no shutdown
!
router bgp 100.4
bgp router-id 10.0.99.4
bgp asnotation dot
bgp log-neighbor-changes
neighbor 10.0.34.3 remote-as 100.3
neighbor 10.0.45.5 remote-as 100.5
!
end
|
R5 のコンフィグ
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17 | hostname R5
!
interface Loopback99
ip address 10.0.99.5 255.255.255.255
!
interface Ethernet0/3
ip address 10.0.45.5 255.255.255.0
no shutdown
!
router bgp 100.5
bgp router-id 10.0.99.5
bgp asnotation dot
bgp log-neighbor-changes
network 10.0.99.5 mask 255.255.255.255
neighbor 10.0.45.4 remote-as 100.4
!
end
|
R1 での状態確認
show ip bgp summary の実行結果は以下の通りです。自 AS は「100.1（6,553,601）」、10.0.12.2 側の AS は「100.2（6,553,602）」と設定されていることが分かります。
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14 | R1# show ip bgp summary
BGP router identifier 10.0.99.1, local AS number 100.1
BGP table version is 4, main routing table version 4
1 network entries using 140 bytes of memory
1 path entries using 80 bytes of memory
1/1 BGP path/bestpath attribute entries using 144 bytes of memory
1 BGP AS-PATH entries using 40 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 404 total bytes of memory
BGP activity 2/1 prefixes, 2/1 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
10.0.12.2 4 100.2 12 10 4 0 0 00:06:19 1
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show ip bgp neighbors の実行結果は以下の通りです。「Neighbor capabilities:」欄に「Four-octets ASN Capability: advertised and received」とあるので、OPEN Message のやりとりでお互いの Capability を確認し合った結果、「両ルータともに 4 バイト AS 対応している」と認識されていることが分かります。
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108 | R1# show ip bgp neighbors
BGP neighbor is 10.0.12.2, remote AS 100.2, external link
BGP version 4, remote router ID 10.0.99.2
BGP state = Established, up for 00:06:39
Last read 00:00:15, last write 00:00:09, hold time is 180, keepalive interval is 60 seconds
Neighbor sessions:
1 active, is not multisession capable (disabled)
Neighbor capabilities:
Route refresh: advertised and received(new)
Four-octets ASN Capability: advertised and received
Address family IPv4 Unicast: advertised and received
Enhanced Refresh Capability: advertised and received
Multisession Capability:
Stateful switchover support enabled: NO for session 1
Message statistics:
InQ depth is 0
OutQ depth is 0
Sent Rcvd
Opens: 1 1
Notifications: 0 0
Updates: 1 2
Keepalives: 9 8
Route Refresh: 0 0
Total: 11 13
Default minimum time between advertisement runs is 30 seconds
For address family: IPv4 Unicast
Session: 10.0.12.2
BGP table version 4, neighbor version 4/0
Output queue size : 0
Index 2, Advertise bit 0
2 update-group member
Slow-peer detection is disabled
Slow-peer split-update-group dynamic is disabled
Sent Rcvd
Prefix activity: ---- ----
Prefixes Current: 0 1 (Consumes 80 bytes)
Prefixes Total: 0 1
Implicit Withdraw: 0 0
Explicit Withdraw: 0 0
Used as bestpath: n/a 1
Used as multipath: n/a 0
Outbound Inbound
Local Policy Denied Prefixes: -------- -------
Bestpath from this peer: 1 n/a
Total: 1 0
Number of NLRIs in the update sent: max 0, min 0
Last detected as dynamic slow peer: never
Dynamic slow peer recovered: never
Refresh Epoch: 2
Last Sent Refresh Start-of-rib: never
Last Sent Refresh End-of-rib: never
Last Received Refresh Start-of-rib: 00:06:39
Last Received Refresh End-of-rib: 00:06:39
Refresh-In took 0 seconds
Sent Rcvd
Refresh activity: ---- ----
Refresh Start-of-RIB 0 1
Refresh End-of-RIB 0 1
Address tracking is enabled, the RIB does have a route to 10.0.12.2
Connections established 2; dropped 1
Last reset 00:07:37, due to BGP Notification received, CEASE: unknown subcode
Transport(tcp) path-mtu-discovery is enabled
Graceful-Restart is disabled
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 1
Local host: 10.0.12.1, Local port: 32329
Foreign host: 10.0.12.2, Foreign port: 179
Connection tableid (VRF): 0
Maximum output segment queue size: 50
Enqueued packets for retransmit: 0, input: 0 mis-ordered: 0 (0 bytes)
Event Timers (current time is 0xD5A72):
Timer Starts Wakeups Next
Retrans 11 0 0x0
TimeWait 0 0 0x0
AckHold 10 7 0x0
SendWnd 0 0 0x0
KeepAlive 0 0 0x0
GiveUp 0 0 0x0
PmtuAger 1 0 0x106A4B
DeadWait 0 0 0x0
Linger 0 0 0x0
ProcessQ 0 0 0x0
iss: 476279476 snduna: 476279728 sndnxt: 476279728
irs: 3926202530 rcvnxt: 3926202869
sndwnd: 16133 scale: 0 maxrcvwnd: 16384
rcvwnd: 16046 scale: 0 delrcvwnd: 338
SRTT: 770 ms, RTTO: 2360 ms, RTV: 1590 ms, KRTT: 0 ms
minRTT: 1 ms, maxRTT: 1000 ms, ACK hold: 200 ms
Status Flags: active open
Option Flags: nagle, path mtu capable
IP Precedence value : 6
Datagrams (max data segment is 1460 bytes):
Rcvd: 21 (out of order: 0), with data: 11, total data bytes: 338
Sent: 22 (retransmit: 0, fastretransmit: 0, partialack: 0, Second Congestion: 0), with data: 11, total data bytes: 251
Packets received in fast path: 0, fast processed: 0, slow path: 0
fast lock acquisition failures: 0, slow path: 0
TCP Semaphore 0xF342950C FREE
|
show ip bgp の実行結果は以下の通りです。R5 が広報している「10.0.99.5/32」が確認出来ます。
| R1# show ip bgp
BGP table version is 4, local router ID is 10.0.99.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
Network Next Hop Metric LocPrf Weight Path
*> 10.0.99.5/32 10.0.12.2 0 100.2 100.3 100.4 100.5 i
|
パケットキャプチャ
R1 でパケットキャプチャした結果は以下の通りです。
OPEN Message
R1 → R2 向きに送信した OPEN Message をキャプチャした結果は以下の通りです。「4 バイト AS」は「4 バイト AS 非対応のルータとも相互運用出来ること」を目指して設計されている為、従来の「My AS」フィールドは（実際の設定に関わらず）常に『23,456』です。Open Message で Optional Parameter（Capability）を交換する際に Type 65 として定義されている「Support for 4-octet AS number capability」を両方のルータで認識出来た場合、4 バイト AS が利用されます。その場合、利用する 4 バイト長の AS 番号は Type 65 の Optional Parameter の中で定義されています。
UPDATE Message
R2 → R1 向きに送信した UPDATE Message をキャプチャした結果は以下の通りです。UPDATE Message 中に含まれる AS Path Attribute も 4 バイト AS で表現されているのが分かります。
