recently i connect to my postfix server become very slowly,
eg: my ip address is 10.1.1.1, and the postfix server's ip is 172.16.1.1,
i type ' telnet 172.16.1.1 25' and wait for more than 15 seconds to get the response from the postfix server, this is the log of postfix:
May 13 18:28:25 serv01 postfix/smtpd[15625]: connection established
May 13 18:28:25 serv01 postfix/smtpd[15625]: master_notify: status 0
May 13 18:28:25 serv01 postfix/smtpd[15625]: name_mask: resource
May 13 18:28:25 serv01 postfix/smtpd[15625]: name_mask: software
May 13 18:28:37 serv01 postfix/smtpd[15625]: connect from unknown[10.1.1.1] ####### here , nothing happen ,but consuming 12 seconds!!!
May 13 18:28:37 serv01 postfix/smtpd[15625]: match_list_match: unknown: no match
May 13 18:28:37 serv01 postfix/smtpd[15625]: match_list_match: 10.1.1.1: no match
May 13 18:28:37 serv01 postfix/smtpd[15625]: match_list_match: unknown: no match
May 13 18:28:37 serv01 postfix/smtpd[15625]: match_list_match: 121.8.17.183: no match
May 13 18:28:37 serv01 postfix/smtpd[15625]: match_hostname: unknown ~? 127.0.0.0/8
May 13 18:28:37 serv01 postfix/smtpd[15625]: match_hostaddr: 10.1.1.1 ~? 127.0.0.0/8

strangely , i try to telnet my server for several times , every time it take 12 seconds to connect.
can any guys tell me please, why it consumed 12 seconds ,and what happen ?

Perhaps a routing issue. Post your routes from both servers (netstat -r should show them).

client:
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
10.1.1.0 * 255.255.255.0 U 0 0 0 eth0
169.254.0.0 * 255.255.0.0 U 0 0 0 eth0
default 10.1.1.254 0.0.0.0 UG 0 0 0 eth0

server:
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
172.16.1.0 * 255.255.255.0 U 0 0 0 eth0
169.254.0.0 * 255.255.0.0 U 0 0 0 eth0
default 172.16.1.1 0.0.0.0 UG 0 0 0 eth0

when i run 'netstat -r ' in server, it display the line '169.254.0.0 ....', then stop about 15 secondes, finally display the line 'default ......'

but when i run 'netstat -nr', it response very fast

btw: i run 'arp ' in server, it response very slow too

hi, i think i got the key, one of the dns server was down, so it take a long time to resolve the name, thanks for reply me

Yes, if the first DNS server a system checks is down then it goes on to the 2nd one. But it's a lengthy delay as you've observed.

Arp, which another poster mentioned, is only used for discovery in the local sub-net. That's not the situation here.