BGP Default-Originate insights

BGP has multiple ways of advertising a default route to its neighbors;  the neighbor default-originate command is one of these methods and used to advertise a default route to a specific neighbor. Below are some characteristics of the default route advertised by this way. Originator router: Default route does not need to be existing in the routing or BGP table before advertising. The default route will not be installed in the BGP table as local. The default does not appear in the output of the command show of the advertised routes. The route can not be filtered outbound by the …

Read More »

Per packet vs Per destination load balancing

Per packet load balancing: This method allows traffic distribution on a round robin fashion as stated in the previous post, this means that With per-packet load balancing enabled, the router sends one packet for destinationA over the first path, the second packet for the same destination over the second path, and so on. Per packet load balancing is used to avoid path congestion and for insuring equal utilization for all paths to the same destination. However it may result in out-of-order packets in the data stream which may introduce some problems to sensitive applications like voice or video. This method …

Read More »

Load balancing in a nutshell

Load balancing is the action of distributing traffic over multiple paths. The router automatically load balances traffic if it has multiple routes to the same destination in the routing table. RIP, OSPF and ISIS supports only equal cost load balancing, this means that in order to install multiple routes in the routing table they must have the same metric. EIGRP and EBGP support unequal cost load balancing. The command maximum-paths defines how many paths can concurrently exist for the same prefix in the routing table. To disable load balancing issue the command maximum-paths 1. Load balancing can be on per …

Read More »

Inter-AS MPLS VPN – The whole story (1) – Updated Dec 2008

The IETF released the first RFC for MPLS L3VPNs; RFC 2547, “BGP/MPLS VPNs” in 1999 as a standardized form for the emerging Cisco’s tag switching at that time, succeeded with revised drafts in 2003, 2004 and 2005; draft-ietf-2547bis, mainly adding Inter-Domain MPLS L3VPNs (Multi-AS backbone (Inter-AS) and Carriers’ Carriers), and was finally approved and RFC 2547 was obsolete in 2006 with RFC 4364, “BGP/MPLS IP Virtual Private Networks (VPNs)”.

Read More »

System MTU explained

By default any interface on the switch can only send or receive a frame of a maximum size 1500 byte. Some applications like (QinQ, MPLS over Ethernet) require increasing the MTU of the switches in your network to allow greater sizes because thier frames may exceed the default 1500 bytes size. You can increase the MTU of all interfaces operating at 10/100 Mbits using the command system mtu <vlaue>. This command will not affect GigaEthernet ports; the command system mtu jumbo may be used to alter the MTU of the GigaEthernet interfaces. You will need to reload the switch for …

Read More »

What is: a voice VLAN port?

A voice VLAN port is an access port attached to a Cisco IP Phone, configured to use one VLAN for voice traffic and another VLAN for data traffic from a device attached to the phone. This feature allows the switch to use CDP for sending configuration options regarding COS, Voice VLAN and data VLAN to the IP Phone. This feature is disabled by default and the IP Phone sends both voice and data traffic in the default VLAN (VLAN 0). you can use CISCO documentation for more details about this feature.

Read More »