CiscoNET

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Part I

So slow Internet connection after scheduled maintenance on upstream provider(ISP). It could be multiple reasons such as software issue, hardware failure, bad patch cable , dirty fiber and trunk issue. Those are very rare case. Lately I noticed more trouble with MTU mis-setting on backbone routers. When ISP expends their backbone trunk, they put TenGigE card instead of SONET in these days. No wonder why they do that b/c GigE or TenGigE card is much cheaper then SONET card.

Here is common mistake is that the forget to change default MTU size(1500) of the fresh card from the box. Most of ISP set MTU on their backbone as upto 9180 or at least bigger than 1524 bytes (due to VLAN tag for internal use). Again, this is very rare case, but it happens. See how to verify MTU size wrong in the ISP backbone.

Here is the sample configuration to allow traceroute(Unix or Network devices) and tracert(MS Windows)

"TraceRoute" commands of Unix and Cisco devices send UDP packets, while "TraceRT" commands in MS Windows is sending ICMP packets.
In both cases the returning packets are only ICMP. For "TraceRT".

Cisco Router#
Cisco Router#conf t
Cisco Router(config)#access-list 111 permit icmp any any time-exceeded
Cisco Router(config)#access-list 111 permit icmp any any unreachable or port-unreachable 

If you want to accept ping (ICMP echo-reply), it would be like below

Cisco Router#
Cisco Router#conf t
Cisco Router(config)#access-list 111 permit icmp any any echo-reply ; (ICMP type 0)
Cisco Router(config)#access-list 111 permit icmp any any time-exceeded
Cisco Router(config)#access-list 111 permit icmp any any unreachable or port-unreachable ; (ICMP type 3)

Then, apply WAN Serial interface(in this example)

Cisco Router#
Cisco Router#conf t
Cisco Router(config)#interface serial1/1
Cisco Router(config-if)#ip access-group 111 in

* If you have outbound ACL, you need to allow UDP and ICMP echo. If you have inbound policy, then you don't need below.

Cisco Router(config)#access-list 111 permit UDP any any gt 3000
Cisco Router(config)#access-list 111 permit icmp any any echo ; Echo request (type 8)
 

 ** If you see below output, it is evidence of missing "time-exceeded (ICMP type 11)"

Cisco Router#tr 200.200.200.1

Type escape sequence to abort.
Tracing the route to 200.200.200.1

  1 100.100.100.2 24 msec 24 msec 8 msec
  2  *  *  *
  3  *  *  *
  4  *  *  *
  5  *  *  *
  6 200.200.200.1 44 msec 52 msec *
Cisco Router#
 

Here is quick guide of "How to restore Firefox default setting"

1. From bottom status bar, click Start > Run and put " firefox.exe -safe-mode "

Here is useful tips to reduce Firefox high memory usage. Before changing options, you are better to save previous option in case any issues.

Here is the Firefox 3.6 memory usage before changes by Taskmgr. As you can see Firefox is taking 252M. Let's see how much we can reduce Firefix high memory usage after modification.