Cisco banner usage

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 [...]

Bridging Ethernet over an IP network using DLSw+

While surfing through the internet, i found a nice feature called DLSw+. I must admit, that i never heard about it before, although it’s a really old feature.
DLSw (Data Link Switching) originally was developed to transport IBM Systems Network Architecture (SNA) and IBM NetBIOS over routed IP networks. But you can also use it for [...]

Bridging across GRE tunnels (experimental)

In former posts, i already mentioned the flexibility of GRE tunnels.
A few days ago, i tried to assign a Tunnel interfaces to a bridge-group to get Layer-2 conectivity between 2 sites.
Unexpectedly, it works, although bridge-group commands aren’t supported on Tunnel interfaces.
Here`s a small image, to illustrate the setup

The setup in this example is using  c3725-adventerprisek9-mz.124-15.T6.bin [...]

PPPoE dialin with a Cisco 871/876/878

The Cisco 871/876 is a small SOHO router with an integrated four-port switch on the LAN side.
On the WAN side, the C871 provides a Fastethernet interface for connecting an external xDSL-Modem, while C876/C878 have integrated xDSL-Modems available. C876 provides the ADSL Annex B flavor, the C878 offers an SHDSL-Modem.
Here are two templates for PPPoE dialin to an ISP.
Traffic from internal LAN is natted [...]

Configuring a Multichannel STM-1 on a Cisco router

When you have numerous E1 customers (> 8), you could terminate them on dedicated E1 ports of a router, e.g. with one or more  PA-MC-8E1/120 (EoL since 2003).
A more efficient way is to terminate them on a STM-1 port-adapter (e.g. a PA-MC-STM1), where you can aggregate up to 63 customers with one single fiber connection to the transport [...]

SDH multiplex structure

 Synchronous Digital Hierarchy (SDH) is a CCITT standard for a hierarchy of optical transmission rates. Synchronous Optical Network (SONET) is an ANSI (American National Standards Institute) standard for North America, that is largely equivalent to SDH.
Both are widely spread technologies for very high speed transmission of voice and data signals across the numerous world-wide fiber-optic networks.
SDH and SONET are [...]

Setting up a Cisco router for terminating Microsoft L2TP IPSec sessions

For this example i used a Cisco 1841 running c1841-advsecurityk9-mz.124-3i.bin

Remote User connects to gate’s puplic reachable IP with his Microsoft L2TP IPSec client (Windows 2000 and higher)
After successful authentication, the Client gets an IP address from local pool
MS L2TP-IPSec-Client adds a default route over the new PPP interface (but you can deactivate it)

Here’s the template for router [...]

Administrative distance / Route preference

Juniper and Cisco use different values for the administrative distance of routes from specific Routing protocols.
To illustrate the differences, i will show two tables taken directly from the vendors homepages.
(taken from Cisco website)

Route Source
Default Distance Values

Connected interface

Static route

Enhanced Interior Gateway Routing Protocol (EIGRP) summary route

External Border Gateway Protocol (BGP)

Internal EIGRP



Intermediate System-to-Intermediate System (IS-IS)

Routing Information Protocol (RIP)

Exterior [...]

JunOS route selection

(taken from Juniper website)
How the Active Route Is Determined
For each prefix in the routing table, the routing protocol process selects a single best path, called the active route. The algorithm for determining the active route is as follows:

Choose the path with the lowest preference value (routing protocol process preference). Routes that are not eligible to [...]

Syslog facilities and priorities

syslog is the most common protcol for transmitting system messages over an IP network.
It is described at length in RFC 3164.
At the bottom of the post, you can find the meanings of syslog facility and severity (also known as priority)
Layout of a syslog message

Name of program

Note: Not all parts are visible in the logfile(s), but [...]