UPDATE Packing
Quick review on BGP UPDATEs
+-----------------------------------------------------+
| Withdrawn Routes Length (2 octets) |
+-----------------------------------------------------+
| Withdrawn Routes (variable) |
+-----------------------------------------------------+
| Total Path Attribute Length (2 octets) |
+-----------------------------------------------------+
| Path Attributes (variable) |
+-----------------------------------------------------+
| Network Layer Reachability Information (variable) |
+-----------------------------------------------------+
At the top you list a combination of attributes (MED = 50, Local Pref = 200, etc)
Then you list all of the NLRI (prefixes) that share this combination of attributes