I have confusion with regard to Juniper MPLS LSP unequal cost balancing. In Juniper we can define 2 or more LSPs between R1 and R2. With some LSPs taking the IGP best path (default behavior) while for other LSPs we can define ERO so that take alternate path to same destination. This is done to avoid congestion and to optimize network resources by utilizing multiple links.

We also configure 'load balance per packet' under routing-options in JUNOS shown below:-

R1> show configuration routing-options forwarding-table 
export ecmp;

R1> show configuration policy-options policy-statement ecmp 
term load-balance {
    then {
        load-balance per-packet;

Now we have learnt that load balancing occurs when there are multiple 'equal' cost paths to same destination.

However in our case we have multiple LSPs to same destination. For some LSPs CSPF metric is shown less while for other LSPs metric is shown large (those with ERO defined) via command ' show mpls lsp extensive'. But traffic is load balanced across all LSPs (We are using auto bandwidth LSPs which shows bandwidth along with other parameters). So auto LSPs shows that bandwidth across each LSP is more or less same.

  1. How is load balancing happening among all LSPs (between same ingress/egress) when CSPF metric of LSPs is shown different.

  2. Does the above situation also valid for simple LSPs (that are not Auto bandwidth LSPs)

  3. Does the bandwidth shown by auto bandwidth LSP (show mpls lsp extensive) reflect actual traffic rate between ingress and egress? Meaning traffic rate between R1 and R2 is also same like that shown by auto lsp bandwidth parameter (show mpls lsp extensive). We have not configured bandwidth parameter in our network.

Many Thanks

  • @JordanHead. Sir you posted an article on auto-bandwidth LSPs load balancing. I would high appreciate if you please provide an answer to my query. Thank you very much !!! – NABEEL NASIR Mar 21 at 18:22

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