Probly this may be a very simple quiestion ..in one interview they asked me ...What is EIGRP Stack ? ..i am not sure what xactly it is .... i try to find some docs but cudint find any ..
Can some one help me regarding the same
The protocol number (Assigned by IANA) defines the protocol used in the data portion of the IP datagram , it is simply a numeric identification of the upper layer protocol that an IP packet should be sent to. Stored in the IP header of an IP packet, the most common IP protocol numbers are TCP (6), UDP (17) and ICMP (1), thus in your case when the router sees that the IP protocol number is 88 it understands that this is not a TCP or UDP packet, and that it is an EIGRP packet.
The link provided by Pavlo is IANAs reference for all these numbers.