After an NE5000E is upgraded from V200R003C02B609 to V300R007C00SPC500, GSR traffic on the MAN all flows to the upgraded NE5000E.
The networking is as follows:
582-NE5000E -- 661-NE5000E
1. The GSR (NE80E) establishes IBGP peer relationships with the two NE5000Es. The NE5000Es learn EBGP routing information from their upstream CRS and forward the information to the NE80E.
2. When the NE80E receives two IBGP routes from the two NE5000Es, it compares the next-hop information of the two routes. The next hop of one route is the loopback address on one NE5000E, and the next hop of the other route is the loopback address on the other NE5000E.
3. The cost of the OSPF route to the loopback address on the NE5000E (581) is 4, and that of the OSPF route to the loopback address on the NE5000E (661) is 5. BGP compares the two routes in terms of the costs of IGP routes to their respective next-hop addresses and finds that the BGP route to the NE5000E (582) is better. As a result, all traffic flows to the NE5000E (582).
In V300R007C00SPC500, the costs of loopback interfaces are not counted in OSPF route cost calculation. In V200R003C02B609, however, the cost of each loopback interface is counted as 1 in OSPF route cost calculation.
1. If two NE5000Es are deployed on a MAN and only one of them is upgraded, you can run the OSPF cost 1 command on the loopback interface of the upgraded NE5000E.
2. Learn the differences between versions before the upgrade. In VRP V500R007 (for NE40E/NE80E V600R001 and NE5000E V300R007) and later VRP versions, the cost of loopback interfaces in OSPF is 0.