Methods and arrangements for configuring the L2GPs in a first STP domain connected towards a second STP domain
Embodiments of the present invention relate to methods and arrangements for configuring the L2GPs in a first STP domain connected towards a second STP domain such that L2GPs in the first STP domain are assigned with the same Pseudo Root identity. Thus the Pseudo Root identity does not have to be changed if one of the L2GPs goes down, which implies that count-to-infinity loops may be avoided. It should be noted that only one L2GP is allowed to be open towards the second STP domain. The root path costs are assigned to the L2GPs towards the pseudo root and the value of the root path cost controls which of the L2GPs that should be open. The most preferred L2GP will be given a root path cost=0, the second best L2GP will have a path cost which is high enough so the two ports never will be open at the same time if there is connectivity between the Ethernet switches having the L2GPs.
1. A method in a Spanning Tree Protocol (STP) domain comprising a plurality of Ethernet switches interconnected by links, wherein at least two of the plurality of Ethernet switches comprise ports defined as Layer 2 Gateway Ports (L2GPs), comprising the steps of:
configuring the at least two L2GPs to the same pseudo root outside the STP domain by means of a first emulated connection and a second emulated connection, wherein the emulated connections from the L2GPs to the same pseudo root is achieved by assigning the same pseudo root identity to the L2GPs, and
associating L2GP with a root path cost from the respective L2GP to the pseudo root, wherein the root path cost of the first L2GP differs from the root path cost of the second L2GP to only keep one of the first emulated connection and the second emulated connection open towards the pseudo root, wherein the root path cost of the L2GP is a function of the bandwidth of an associated physical link or physical link aggregation group.
2. The method according to claim 1 , wherein a physical link aggregation group from an Ethernet switch comprises at least two physical links and the root path cost of the L2GP associated with the link aggregation group is dependent on the number of working physical links.
3. A Spanning Tree Protocol (STP) domain comprising a plurality of Ethernet switches interconnected by physical links, wherein at least two of the plurality of Ethernet switches comprise ports defined as Layer 2 Gateway Ports (L2GPs), wherein the at least two Ethernet switches comprising a first L2GP and a second L2GP, respectively, are configured to have emulated connections to the same pseudo root outside the STP domain by means of a first emulated connection and a second emulated connection, respectively, and each of L2GPs is configured with a root path cost from the respective Ethernet switch to the pseudo root, wherein the root path cost of the first L2GPs differs from the root path cost of the second L2GP to only keep one of the first emulated connection and the second emulated connection open towards the pseudo root, wherein the L2GPs of the Ethernet switches are configured to be assigned with the same pseudo root identity to achieve the emulated connections from the L2GPs to the same pseudo root, wherein the root path cost of the L2GP is a function of the bandwidth of an associated physical link or physical link aggregation group.
4. The STP domain according to claim 3 , wherein a physical link aggregation group from an Ethernet switch comprises at least two physical links and the root path cost of the L2GP associated with the link aggregation group is dependent on the number of working physical links.
5. An Ethernet switch for a Spanning Tree Protocol (STP) domain, wherein the STP domain includes a plurality of Ethernet switches interconnected by physical links, wherein the Ethernet switch and at least one further Ethernet switch of the plurality of Ethernet switches of the STP domain comprise ports defined as Layer 2 Gateway Ports (L2GPs) wherein said Ethernet switch is configured to be connected to the same pseudo root outside the STP domain as the further Ethernet switch by means of a first emulated connection and the further Ethernet switch is configured to be connected to said pseudo root outside the STP domain by means of a second emulated connection, the Ethernet switch is further configured to associate a root path cost to its L2GP and to keep track of root path costs of the L2GPs of other Ethernet switches of the STP domain, such that the root path cost of the first L2GP differs from the root path cost of the L2GPs of the other Ethernet switches to only keep one of the first emulated connection and the second emulated connection open towards the pseudo root, wherein the L2GP of the Ethernet switch is configured to be assigned with the same pseudo root identity as the L2GP of the further Ethernet switch to achieve the emulated connections from the Ethernet switches to the same pseudo root, wherein the root path cost of the L2GP is a function of the bandwidth of an associated physical link or physical link aggregation group.
6. The Ethernet switch according to claim 5 , wherein a physical link aggregation group from an Ethernet switch comprises at least two physical links and the root path cost of the L2GP associated with the link aggregation group is dependent on the number of working physical links.