CCNP3 BCMSNImplementing Inter-VLAN routing

Router on at stick og inter-vlan routing.

Multi layer switching

Fordele og ulemper med router on stick.

The advantages are as follows: • Implementation is simple.• Layer 3 services are not required on the switch.• The router provides communications between VLANs.

The disadvantages are as follows:• The router is a single point of failure.• (Passer dog ikke helt man kan lave etcher channel eller lacp på en asa eller router• hvis den her flere lan interfaces.)• The single traffic path between the switch and the router may become congested.• Latency is higher than on a Layer 3 switch.

Router on a stick er lige ude af landevejen.

multilayer switchinghvad er det ?

A routed switch port is a physical switch port on a multilayer switch that is capable of Layer 3 packet processing. A routed port is not associated with a particular VLAN, as contrasted with an access port or SVI. The switch port functionality is removed from the interface. A routed port behaves like a regular router interface, except that it does not support VLAN subinterfaces. Routed switch ports can be configured using most commands applied to a physical router interface, including the assignment of an IP address and the configuration of Layer 3 routing protocols.A routed switch port is a standalone port that is not associated with a VLAN, whereas an SVI is a virtual interface that is associated with a VLAN. SVIs generally provide Layer 3 services for devices connected to the ports of the switch where the SVI is configured. Routed switch ports can provide a Layer 3 path into the switch for a number of devices on a specific subnet, all of which are accessible from a single physical switch port.The number of routed ports and SVIs that can be configured on a switch is not limited by software. However, the interrelationship between these interfaces and other features configured on the switch may overload the CPU because of hardware limitations.

enabling routing between vlan.

Hvad er cef.

Cisco Express ForwardingCEF is mainly used to increase packet switching speed, reducing the overhead and delays introduced by other routing techniques, increasing overall performance. CEF consists of two key components: The Forwarding Information Base (FIB) and adjacencies.The FIB is similar to the routing table generated by multiple routing protocols, maintaining only the next-hop address for a particular IP-route.The adjacency maintains layer 2 or switching information linked to a particular FIB entry, avoiding the need for an ARP request for each table lookup. There are five types of adjacencies:

• Null adjacency: Handles packets destined to a NULL interface. Packets with FIB entries pointing to NULL adjacencies will normally be dropped.

• Punt adjacency: Deals with packets that require special handling or can not be switched by CEF. Such packets are forwarded to the next switching layer (generally fast switching) where they can be forwarded correctly.

• Glean adjacency: Handles packets destined for currently attached hosts, but without layer 2 information.• Discard adjacency: FIB entries pointing to this type of adjacency will be discarded.• Drop adjacency: Packets pointing to this entry are dropped, but the prefix will be checked.

In order to take full advantage of CEF, it is recommended to use distributed CEF (dCEF), where there is a FIB table on each of the line cards. This avoids the need for querying the main processor or routing table in order to get the next-hop information, performing the fast switching on the line card itself.CEF currently supports Ethernet, Frame Relay, ATM, PPP, FDDI, Tunnels and HDLC. Cisco Express Forwarding (CEF) is deployed to facilitate Layer 3 switching through hardware-based tables, switch virtual interfaces (SVIs)trunks  This single physical link must be Fast Ethernet or greater to support Inter-Switch Link (ISL) encapsulation, but 802.1Q is supported on 10-Mbps Ethernet router interfaces. Multilayer switches forward frames and packets at wire speed by using application-specific integrated circuit (ASIC) hardware. Specific Layer 2 and Layer 3 components, such as routing tables or access control lists (ACLs), are cached into hardware. These tables are stored in content-addressable memory (CAM) and ternary content-addressable memory (TCAM).

Cisco Express Forwarding (CEF) is deployed to facilitate Layer 3 switching through hardware-based tables, switch virtual interfaces (SVIs)trunks  This single physical link must be Fast Ethernet or greater to support Inter-Switch Link (ISL) encapsulation, but 802.1Q is supported on 10-Mbps Ethernet router interfaces. Multilayer switches forward frames and packets at wire speed by using application-specific integrated circuit (ASIC) hardware. Specific Layer 2 and Layer 3 components, such as routing tables or access control lists (ACLs), are cached into hardware. These tables are stored in content-addressable memory (CAM) and ternary content-addressable memory (TCAM).

Layer 3 switching can occur at two different locations on the switch: • Centralized: Switching decisions are made on the route processor by a central forwarding table, typically controlled by an

ASIC. • Distributed: Switching decisions are made on a port or line-card level. Cached tables are distributed and synchronized to

various hardware components so that processing can be distributed throughout the switch chassis.

Layer 3 switching uses one of these two methods, depending on the platform: • Route caching: Also known as flow-based or demand-based switching, a Layer 3 route cache is built in hardware, since the

switch sees traffic flow into the switch.• Topology-based: Information from the routing table is used to populate the route cache regardless of traffic flow. The

populated route cache is called the forwarding information base (FIB). CEF builds the FIB.•  • Cisco Layer 3 devices can use a variety of methods to switch packets from one port to another. The most basic method of

switching packets between interfaces is called process switching. Process switching moves packets between interfaces on a scheduled basis, based on information in the routing table and the Address Resolution Protocol (ARP) cache. As packets arrive, they are put in a queue to wait for further processing. When the scheduler runs, the outbound interface is determined, and the packet is switched. Waiting for the scheduler introduces latency.

• To speed the switching process, strategies exist to switch packets on demand as they arrive and to cache the information necessary to make packet-forwarding decisions.

• CEF uses these strategies to expediently switch data packets to their destination. It caches information generated by the Layer 3 routing engine. CEF caches routing information in one table (the FIB), and caches Layer 2 next-hop addresses for all FIB entries in an adjacency table. Because CEF maintains multiple tables for forwarding information, parallel paths can exist and enable CEF to load balance per packet.

• CEF operates in one of two modes.• Central CEF: The FIB and adjacency tables reside on the route processor, and the route processor performs the express

forwarding. Use this mode when line cards are not available for CEF switching, or when features are not compatible with distributed CEF.

• Distributed CEF (dCEF): Supported only on Cisco Catalyst 6500 switches. Line cards maintain identical copies of the FIB and adjacency tables. The line cards can perform the express forwarding by themselves, relieving the main processor of being involved in the switching operation. Distributed CEF uses an interprocess communications (IPC) mechanism to ensure that the FIBs and adjacency tables are synchronized on the route processor and line cards

Cisco Layer 3 devices can use a variety of methods to switch packets from one port to another. The most basic method of switching packets between interfaces is called process switching. Process switching moves packets between interfaces on a scheduled basis, based on information in the routing table and the Address Resolution Protocol (ARP) cache. As packets arrive, they are put in a queue to wait for further processing. When the scheduler runs, the outbound interface is determined, and the packet is switched. Waiting for the scheduler introduces latency. To speed the switching process, strategies exist to switch packets on demand as they arrive and to cache the information necessary to make packet-forwarding decisions. CEF uses these strategies to expediently switch data packets to their destination. It caches information generated by the Layer 3 routing engine. CEF caches routing information in one table (the FIB), and caches Layer 2 next-hop addresses for all FIB entries in an adjacency table. Because CEF maintains multiple tables for forwarding information, parallel paths can exist and enable CEF to load balance per packet.CEF operates in one of two modes.

• Central CEF: The FIB and adjacency tables reside on the route processor, and the route processor performs the express forwarding. Use this mode when line cards are not available for CEF switching, or when features are not compatible with distributed CEF.

• Distributed CEF (dCEF): Supported only on Cisco Catalyst 6500 switches. Line cards maintain identical copies of the FIB and adjacency tables. The line cards can perform the express forwarding by themselves, relieving the main processor of being involved in the switching operation. Distributed CEF uses an interprocess communications (IPC) mechanism to ensure that the FIBs and adjacency tables are synchronized on the route processor and line cards.