How does GVRP work?

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Article ID: 5237 


Some background about GVRP:
  • GVRP (Generic VLAN Registration Protocol) actions may be viewed as dynamic VLAN creation accompanied by dynamic, tagged egress permissions for the ingress port through which the given VLAN was learned.
  • Though the resulting functionality could be similar to that seen on a 802.1Q Trunk, ports are not automatically put into "802.1Q Trunk mode" for those products supporting such a mode.
  • GVRP starts with knowledge of one or more VLANs egressing ethernet-linked ports, then advertises these VLAN IDs to neighboring switches, propagating dynamic 802.1Q VLAN registration packets between GVRP-aware ports. Upon receipt, any VLAN IDs not already known to the receiving switch are created dynamically, and enabled for tagged egress on the receiving port only.
      Note: On the SecureStack, all local VLANs are initially advertised - not just those with at least one active port egress (11670).
    • All GVRP-aware switches perform this same function, while also relaying the GVRP advertisements of others. Ultimately, all GVRP-aware switches should contain much the same VLANs -- some Static (manually configured), and some Dynamic (created via GVRP).
    • Functionally, it is then possible to configure, onto perimeter switches on opposite ends of the network, a user port to egress a new VLAN - and GVRP will dynamically create a "tunnel" to propagate that VLAN, end-to-end. The intermediate switches need not have ports egressing these VLANs, in order for the GVRP relay to function.
    • When all active egress for a VLAN has been removed from a switch, its direct advertisement of that VLAN will cease, and any GVRP-learned knowledge of that VLAN will time out unless reinforced by other switches with direct knowledge of the same VLAN.
    • When using GVRP over a 802.1Q Trunk port, be aware that GVRP itself is propagated without VLAN tags (and GVRP packets are themselves not associated with - or assigned to - a VLAN). Thus, for it to work, the receiving port must not be configured to filter untagged frames. Typically, a 802.1Q Trunk port does in fact filter untagged frames by default.
    • It is possible to use only a single switch as a Static VLAN "point source", rather than using two or more perimeter switches for this purpose; if the remaining switches are SmartSwitch 2000/6000 2nd/3rd Generation, with all Inter-Switch Links configured as 802.1Q Trunks but permitted to accept both tagged and untagged frames. Whenever a VLAN is learned dynamically on these switches via incoming untagged GVRP advertisements, the VLAN automatically gets tagged egress on all the switches' 802.1Q Trunks - a very nice flexiblity.
    • Even on devices which support tag insertion/removal on the ATM link, all the VLANs which traverse a given ELAN (this is not a problem for PVCs) must share a single FID. This is due to the fact that ATM LE_ARPs do not contain VLAN information, ever.
    GVRP may be classed with GMRP (Generic Multicast Regstration Protocol) as both using the Generic Attribute Registration Protocol (GARP). 

    See also: 5462.
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    Posted 4 years ago

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