BGP session through Cisco ASA

You can configure MD5 authentication between two BGP peers, which means that each segment sent on the TCP connection between the peers is verified. MD5 authentication must be configured with the same password on both BGP peers; otherwise, the connection between them will not be made. The configuration of MD5 authentication causes Cisco IOS software to generate and check the MD5 digest of every segment sent on the TCP connection. If authentication is invoked and a segment fails authentication, then an error message will be displayed in the console.

When you are configuring BGP peers with MD5 authentication that pass through a PIX firewall, it is important to configure the PIX between the BGP neighbors so that the sequence numbers for the TCP flows between the BGP neighbors are not random. This is because the TCP random sequence number feature on the PIX firewall is enabled by default, and it changes the TCP sequence number of the incoming packets before it forwards them.

MD5 authentication is applied on the TCP psuedo-IP header, TCP header and data (refer to RFC 2385). TCP uses this data—which includes the TCP sequence and ACK numbers—along with the BGP neighbor password to create a 128 bit hash number. The hash number is included in the packet in a TCP header option field. By default, the PIX offsets the sequence number by a random number, per TCP flow. On the sending BGP peer, TCP uses the original sequence number to create the 128 bit MD5 hash number and includes this hash number in the packet. When the receiving BGP peer gets the packet, TCP uses the PIX-modified sequence number to create a 128 bit MD5 hash number and compares it to the hash number that is included in the packet.

The hash number is different because the TCP sequence value was changed by the PIX, and TCP on the BGP neighbor drops the packet and logs an MD5 failed message.

R2–65.1.200.2—–ASA——-65.1.4.4—–R4

ASA CONFIGURATION: (extra norandomseq)

access-list OUTSIDE extended permit tcp any any eq bgp log

tcp-map BGP

tcp-options range 19 19 allow

static (inside,outside) 65.1.4.2 65.1.200.2 netmask 255.255.255.255 norandomseq

static (outside,inside) 65.1.200.4 65.1.4.4 netmask 255.255.255.255 norandomseq

access-group OUTSIDE in interface outside

class-map BGP
match port tcp eq bgp
policy-map global_policy
class inspection_default
inspect dns preset_dns_map
inspect ftp
inspect h323 h225
inspect h323 ras
inspect netbios
inspect rsh

inspect rtsp
inspect skinny
inspect esmtp
inspect sqlnet
inspect sunrpc
inspect tftp
inspect sip
inspect xdmcp
class BGP
set connection random-sequence-number disable
set connection advanced-options BGP
service-policy global_policy global

The BGP session is fine without password. As soon as enter the command neighbor x.x.x.x password cisco, thing not working.
DEBUG IP TCP TRANSACTION ON ROUTER:

*Jul 2 04:56:53.451: BGP: 65.1.4.2 open active, local address 65.1.4.4

*Jul 2 04:56:53.451: TCB66151E74 created

*Jul 2 04:56:53.451: TCB66151E74 setting property TCP_WINDOW_SIZE (0) 6615C160

*Jul 2 04:56:53.451: TCB66151E74 setting property TCP_MD5KEY (5) 66002A00

*Jul 2 04:56:53.451: TCB66151E74 setting property TCP_TOS (11) 6615C140

*Jul 2 04:56:53.451: TCB66151E74 setting property TCP_OUT_TTL (24) 66150EFA

*Jul 2 04:56:53.451: TCP: Random local port generated 27487, network 0

*Jul 2 04:56:53.451: TCB66151E74 bound to 65.1.4.4.27487
*Jul 2 04:56:53.451: Reserved port 27487 in Transport Port Agent for TCP IP type 1
*Jul 2 04:56:53.451: TCP: sending SYN, seq 1925459762, ack 0
*Jul 2 04:56:53.451: TCP0: Connection to 65.1.4.2:179, advertising MSS 1440

*Jul 2 04:56:53.451: TCP0: state was CLOSED -> SYNSENT [27487 -> 65.1.4.2(179)]

*Jul 2 04:56:55.451: 65.1.4.4:27487 <—> 65.1.4.2:179 congestion window changes
*Jul 2 04:56:55.451: cwnd from 1440 to 1440, ssthresh from 65535 to 2880
*Jul 2 04:56:55.451: TCP0: timeout #1 - timeout is 4000 ms, seq 1925459762
*Jul 2 04:56:55.451: TCP: (27487) -> 65.1.4.2(179)
*Jul 2 04:56:59.451: TCP0: timeout #2 - timeout is 8000 ms, seq 1925459762

*Jul 2 04:56:59.451: TCP: (27487) -> 65.1.4.2(179)

*Jul 2 04:57:00.907: %TCP-6-BADAUTH: Invalid MD5 digest from 65.1.4.2(12644) to 65.1.4.4(179)

*Jul 2 04:57:00.907: TCP0: bad seg from 65.1.4.2 — Invalid MD5 string: port 179 seq 1857634658 ack 0 rcvnxt 0 rcvwnd 16384 len 0

*Jul 2 04:57:07.451: TCP: (27487) -> 65.1.4.2(179)

*Jul 2 04:57:23.451: TCP0: state was SYNSENT -> CLOSED [27487 ->65.1.4.2(179)]

*Jul 2 04:57:23.451: Released port 27487 in Transport Port Agent for TCP IP type 1 delay 240000

*Jul 2 04:57:23.451: TCB 0×66151E74 destroyed

*Jul 2 04:57:23.451: BGP: 65.1.4.2 open failed: Connection timed out; remote host not responding, open active delayed 29552ms (35000ms max, 28% jitter)

The right way is not to NAT! Use static identity NAT or no nat-control.

access-list BGP-MD5-ACL remark *** Allow BGP MD5 Authentication ****
access-list BGP-MD5-ACL permit tcp host 172.16.13.4 host 172.16.11.1 eq bgp

!— Access list allows BGP traffic to pass from outside to inside.

access-group BGP-MD5-ACL in interface outside

tcp-map BGP-MD5
tcp-options range 19 19 allow
!
class-map BGP-MD5-CLASSMAP
match access-list BGP-MD5-ACL
!
policy-map global_policy
class BGP-MD5-CLASSMAP
set connection advanced-options BGP-MD5
set connection random-sequence-number disable
service-policy global_policy global