Single-arm routing, three-layer switching, link aggregation

table of Contents

Single arm routing:

When only the Layer 2 switch needs to realize the communication between different VLANs, one-arm routing is needed.

Link type:

The port that the switch connects to the host is in access mode, and the port that connects to the router is in trunk mode. The physical interface of the router is divided into multiple logical interfaces, and each sub-interface corresponds to a gateway of a VLAN network segment.

Principle: The router re-encapsulates the MAC address and converts the VLAN tag.

Three-layer exchange:

To achieve routing between different VLANs, the Layer 3 switch can be configured with a vlanif interface, and an ip address can be configured through the vlanif interface to become a gateway corresponding to different VLANs, thereby realizing routing between different VLANs.

The principle of the three-layer switching technology: one route, multiple exchanges. When the Layer 3 device receives a data frame, it will re-encapsulate the original data frame with the new source mac address and destination mac address and because the information in the frame header changes, the final frame check CRC should also change accordingly. Among the multiple data packets in this flow, only the first data packet is processed by the three-layer engine of the three-layer switch. The processing method is software, which is the same as the router. The three-layer engine obtains a new layer 2 encapsulation. After the information, route the packet.

After the first data packet is forwarded, an MLS entry is created in the hardware for re-encapsulation and fast forwarding of subsequent data packets performed by the hardware. Layer 2 data frames will be re-encapsulated into the frame format of the next network segment that needs to be forwarded.

There are two forwarding information tables in the MLS entry:
1. The forwarding information database records the host IP address and the VLAN to which it belongs
2. The adjacency table records the host MAC address and switch address

Link aggregation

Port binding technology :

Link Aggregation is a method of bundling a group of physical interfaces together as a logical interface to increase bandwidth. It is also called multi-connection П Load Sharing Group or Link Aggregation Group. Group), by establishing a link aggregation red between two devices, it can provide higher communication bandwidth and higher reliability. Link aggregation provides redundant protection for communication between devices without the need to upgrade hardware.

Conditions for the realization of link aggregation / port aggregation / port binding

1) Each Eth-Trunk interface can contain up to 8 member interfaces.
2) Member interfaces cannot be configured with any services and static MAC addresses.
3) When the member interface is added to the Eth-Trunk, it must be the default hybrid type interface.
4) Eth-Trunk interfaces cannot be nested, that is, member interfaces cannot be Eth-Trunk.
5) An Ethernet interface can only be added to one Eth-Trunk interface. If you need to join other Eth-Trunk interfaces, you must first exit the original Eth-Trunk interface.
6) The member interfaces in an Eth-Trunk interface must be of the same type, for example: FE port and GE port cannot join the same Eth-Trunk interface.
7) Ethernet interfaces on different interface boards can be added to the same Eth-Trunk.
8) If the local device uses Eth-Trunk, the opposite interface directly connected to the member interface must also be bundled as an Eth-Trunk interface, so that both ends can communicate normally.
9) When the rates of member interfaces are inconsistent, the interface with a low rate in actual use may be congested, causing packet loss.
10) After the member interface joins the Eth-Trunk, the MAC address is learned according to the Eth-Trunk, not according to the member interface.