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router looping alarm reported on router after replace EGT2 with EGS4 on OSN equipment

Publication Date:  2012-07-25 Views:  118 Downloads:  0

Issue Description

 Customer configed an  EPL service on EGT2 to connect the LAN Routers,. When we replace EGT2 with EGS4, the router report  looping alarm .

Alarm Information


Handling Process

 Solution 1
 Replace the EGT2 with other transparently transmit boards, but not EGS4
Solution 2
    Disable the port checking on EGS4, The port checking disabled, and STP and RSTP will be transmitted transparently.

in the cause,we choose the solution 2

Root Cause

 Part features of EGT2(related to this issue):
Basic function Transparently transmits 2 x GE services.
Ethernet service type Supports EPL.
MPLS Not supported.
VLAN Supports VLAN transparent transmission.
LPT Supports the LPT in the GFP-carrying mode.
LCAS Dynamically increases or decreases the bandwidth and realizes the protection function, compliant with ITU-T G.7042.
From this table , we could know that the EGT2 supports transparent transmission of Ethernet services; Supports EPL; Supports VLAN transparent transmission; But STP and RSTP are not supported. That is to say: The EGT2 will do nothing to the data package (including the protocol like STP or RSTP)but to transparent transmission only.。
Part features of EGS4 (related to this issue):
Function and Feature EGS4
Basic function Accesses and processes 4 x GE services.
EPL Supports transparent transmission based on port.
  • Supports EVPL services based on port+VLAN. Supports a maximum of 8000 links.
  • Supports EVPL services based on QinQ. Supports service forwarding based on port.
  • Supports the Layer 2 forwarding function and switching at the client and SDH sides.
  • Supports 1k MAC switching or 4k VLAN MAC switching.
  • Supports the function of self-learning the source MAC address. The length of the MAC address table is 128k. The aging time of the MAC address can be set and queried. The configuration of static MAC routes is supported.
  • Supports data isolation based on VB+VLAN.
  • Supports the creation, deletion and query of VB. The maximum number of VBs is 12.
  • Support virtual bridge (VB) + VLAN based data isolation.
  • Supports the setting of a maximum of 4000 VLAN services.
VLAN Supports VLAN and QinQ, the addition, deletion and switching of VLAN labels, compliant with IEEE 802.1q/p.
  • Not supports broadcast packet suppression.
  • Supports RSTP, compliant with IEEE 802.1w.
From this table, we could know that the EGS4 board can support STP and RSTP. Because the customer didn’t enable this function, the data-package will be dealt, then the data part of STP、RSTP would be discarded. So, the loop service will not trigger the RSTP or STP to cut the loop. And alarm appeared.
Test in lab. Replace EGT2 with EGS4: OSN3500 and OSN2500 base on version


Before the board replacement, please check the feature of the board and the version.