Networking Blog

Recently, there was a need for additional FastEthernet ports on a Cisco 1841. The router had already one  HWIC-4ESW attached, but all ports were occupied.
Fortunately, there was a second HWIC-4ESW at stock which was inserted immediately. Two additional ports was configured quickly to a vlan already in use on the other HWIC.
But then the problem [...]

Resilient Ethernet Protocol (REP) is a Cisco propietary protocol which allows you to build redundant Ethernet rings. It’s an alternative to Spanning-Tree protocol and also avoids bridging loops or responds to link failures.
Compared to STP, it offers a faster convergence time (< 300ms) and gives you a simple VLAN load-balancing method.
In our example, we interconnect [...]

I often use the feature interface-range on Cisco switches running IOS.
Not so long ago, i discovered the command interface-range macro, from which i never heard before.
With this macro, you can group several interfaces together and address them by a significant name.
Short example:

define interface-range UPLINKS FastEthernet0/1, FastEthernet0/24
define interface-range USERPORTS FastEthernet0/2 - 23

Usage:

switch#conf t
switch(config)#interface range macro USERPORTS
switch(config-if-range)#switchport [...]

Recently i stumbled across a nice feature in Cisco IOS for building customized menus.
The “menu”-command is really old and was introduced in IOS 10.0
You can i.e. use it for building a menu for CLI-unexperienced staff to simplify troubleshooting.
First of all, you have to configure a little bit AAA  as well as create a user with [...]

When Access Control List Logging is activated on your Cisco device, you will see log entries like that in syslog:

Jun 14 09:49:13 RTR-1 41716: Jun 14 09:49:12.148 MEZ: %SEC-6-IPACCESSLOGP: list 120 denied udp x.x.x.x(1670) -> x.x.x.x(4808), 1 packet
Jun 16 22:14:09 RTR-1 42271: Jun 16 22:14:08.847 MEZ: %SEC-6-IPACCESSLOGDP: list 125 denied icmp x.x.x.x -> x.x.x.x (0/0), [...]

When you deal with Cisco and BGP, you probably know syslog messages like this:

Apr 11 16:34:38 ROUTER 1026843: Apr 11 16:34:38.010 CET: %BGP-3-NOTIFICATION: received from neighbor 80.x.x.x 6/2 (cease) 0 bytes
Apr 17 14:13:41 ROUTER 30082: Apr 17 14:13:41.126 CET: %BGP-3-NOTIFICATION: received from neighbor 80.x.x.x 6/0 (cease) 0 bytes
Apr 27 05:30:39 ROUTER 1028828: Apr 27 05:30:39.833 [...]

Just now, i added a new sticky page to my blog.
It’s a small comparison between Cisco IOS and Juniper JunOS CLI commands.
See here…

(Information taken from j-nsp mailing list and vendors homepages)
MTU Juniper
NOTE: The actual frames transmitted also contain cyclic redundancy check (CRC) bits, which are not part of the media MTU. For example, the media MTU for a Gigabit Ethernet interface is specified as 1500 bytes, but the largest possible frame size is actually 1504 bytes; you [...]

When you use EIGRP as routing protocol, you have two options for filtering advertised routes:

distribute-lists
redistribute-statement with route-map

Received networks can only be filtered out with

distribute-lists

In my simple example, there are 2 routers (R1 and R2) connected via FastEthernet0/1.
Both routers are running EIGRP process 123.

Creating EIGRP process 123 on both routers
With the default configuration, only the link-net [...]

In Cisco IOS, you can use several methods of banners.
The most common methods are:

banner exec
banner login
banner motd

Though all commands use the same syntax
banner motd|login|exec <delimiter> <banner text> <delimiter>
! delimiter is a character, that must not exist in
! the banner message.
there is a different behaviour according to the login method used.
Here’s a table, which shows [...]