Cosine Communications SITA Equant Nortel Networks This draft describes optional sub-TLVs that can be used to extend IGPs to support multiple metrics for use with traffic engineering. These optional extensions are an addendum to the existing work on traffic engineering extensions to OSPF and ISIS. While the current specifications allow advertising only one metric, the ability to advertise multiple metrics has proven to be very useful in similar systems. The encoding for the proposed optional sub-TLVs is also specified.