3com S7906E Instruccion De Instalación

 

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PEs are logically fully meshed (so are PWs), that is, each PE must create for each VPLS 

forwarding instance a tree to all the other PEs of the instance. 

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Each PE must support horizontal split to avoid loops, that is, a PE cannot forward packets via PWs 

of the same VSI, because all the PEs of a VSI are directly connected. In other words, packets from 

PWs on the public network side cannot be forwarded to other PWs; they can only be forwarded to 

the private network side. 

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For PEs in the same VSI, you can configure the remote PE addresses or use an automatic 

discovery mechanism. Currently, LDP and BGP are used to automatically discover VSI peer PEs 

and function as the PW signaling protocol to create PWs. 

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The PW signaling protocol is designed to assign multiplex distinguishing flags (that is, VC labels) 

and advertise the assigned VC flags to the peer. In addition, the PW signaling protocol advertises 

VPLS system parameters such as PW ID, control word, and interface parameters. With the PW 

signaling protocol, fully meshed PWs can be established between PEs for VPLS services. 

The packet encapsulation type of an AC depends on the user VSI access mode, which can be VLAN or 

Ethernet. 

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VLAN access: The Ethernet header of a packet sent by a CE to a PE or sent by a PE to a CE 

includes a VLAN tag that is added in the header as a service delimiter for the service provider 

network to identify the user. The tag is called a P-Tag. 

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Ethernet access: The Ethernet header of a packet upstream from the CE or downstream from the 

PE does not contain any service delimiter. If a header contains a VLAN tag, it is the internal VLAN 

tag of the user and means nothing to the PE. This kind of internal VLAN tag of the user is called a 

U-Tag. 

You can specify the VSI access mode to be used. 

The packet encapsulation type of a PW, also called the PW transport mode, can be either Ethernet or 

VLAN.  

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In Ethernet mode, P-TAG is not transferred on the PW. For a packet from a CE, if it contains the 

service delimiter, the PE removes the service delimiter and adds two levels of MPLS labels into the 

packet before forwarding the packet. Otherwise, the PE directly adds two levels of MPLS labels 

into the packet and then forwards the packet. For a packet to be sent downstream, whether the PE 

adds the service delimiter into the packet depends on your configuration. However, rewriting and 

removing of existing tags are not allowed. 

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In VLAN mode, every packet to the PW must carry a P-TAG. For a packet from a CE, if it contains 

the service delimiter, the PE directly adds two levels of MPLS labels into the packet and sends the 

packet out. Otherwise, the PE adds a null tag together with two levels of MPLS labels into the 

packet and sends the packet out. For a packet to be sent downstream, the PE rewrites, removes, 

or retains the service delimiter depending on your configuration. 

According to the protocol, the packet encapsulation type of a PW is VLAN by default.