Routing Codes

Remember the numerous routing Codes

Some of these as a CCNA and maybe even CCNP you may never use and some say you dont need to know, I beg to differ.

Some of these are crucial, IMHO

Codes:
C - connected
S - static
I - IGRP
R - RIP
M - mobile
B - BGP
D - EIGRP
EX - EIGRP external
O- OSPF
IA - OSPF inter area
N1 - OSPF NSSA external type 1
N2 - OSPF NSSA external type 2
E1 - OSPF external type 1
E2 - OSPF external type 2
E - EGP
i - IS-IS
L1 - IS-IS level-1
L2 - IS-IS level-2
* - candidate default
U - is for user, as in for each user.
ODR - Which = On Demand Routing
P - is for a regularly downloaded static route but I don't know why. So I remember it as "periodic."

E vs D. EGP was probably there first and took the E (it's a legacy protocol)

IA, E1, E2, N1, N2 - this will appear beside an O. So it's either in the area (nothing), or outside the area (IA). If it's an OSPF (E)xternal route, it's either type E1 or E2, again, these are OSPF modifiers. And, for OSPF NSSA's, we've got N1 and N2 routes.

Likewise, i (for IS-IS) has both L1 and L2 routes. Since IGRP had capital I, some DE got smart and used a lowercase.