Routing Protocols Comparison / Subnetting

Detailed info @ CCNP Route - IP Routing Principles

Split-horizon route advertisement is a method of preventing routing loops in distance-vector routing protocols by prohibiting a router from advertising a route back onto the interface from which it was learned.
A--B--C
"A" receive route from "B" about "C" (B know how to reach C).
"A"  will not send this info back to "B", preventing loop if link between "B" and "C" will fail.

Split-horizon routing with poison reverse is a variant of split-horizon route advertising in which a router actively advertises routes as unreachable over the interface over which they were learned by setting the route metric to infinite (16 for RIP).
The effect of such an announcement is to immediately remove most looping routes before they can propagate through the network. The router is said to have poisoned the network by sending 'false' (infinite) metric values to other devices sharing such updates.

With route poisoning, when a router detects that one of its connected routes has failed, the router will poison the route by assigning an infinite metric to it and advertising it to neighbors. When a router advertises a poisoned route to its neighbors, its neighbors break the rule of split horizon and send back to the originator the same poisoned route, called a poison reverse. In order to give the router enough time to propagate the poisoned route and to ensure that no routing loops occur while propagation occurs, the routers implement a hold-down mechanism.


Routing Protocols Comparison Table
Routing protocols - the software that allow routers to dynamically advertise and learn routes, determine which routes are available and which are the most efficient routes to a destination (RIP, EIGRP, OSPF, BGP)
Routed protocols - is a Network Layer protocol that is used to move traffic between networks (IP, IPX, and AppleTalk)
Non-routable protocols - presume that all computers they will ever communicate with are on the same network  (NetBEUI, DLC, LAT, DRP, MOP).

1) Type - exchange routing information within (interior IGP) or between (exterior EGP) an autonomous system (AS).
Autonomous system (AS) - a collection of IP networks and routers under the control of one entity.
2) Convergence - the status of a set of routers having the same knowledge of the surrounding network topology.
3) Protocol Class (Type) - routing algorithms used by varying routing protocols to determine the metric for routing (Distance Vector - Uses hop count, Link State - Uses Shortest Path First, Common View of Network, Hybrid - Distance vector with more accurate update metrics).
4) Administrative distance (AD) - preference of routing protocol - is how a router determines which source of routes it should use if it has two identical routes from different sources. In other words, the router needs to be able to determine which routes to trust if it's receiving the same information from two different sources (which is most trustworthy). The lower the administrative distance - is best
5) Metric - Routers use various metrics and calculations to determine the best route for a packet to reach its final network destination. Each routing protocol uses its own algorithm with varying weights to determine the best possible path (only one from all).
6) Classful routing protocols do not carry subnet mask information on their routing updates  the same subnet mask everywhere is needed to avoid routing black holes),
Classless routing protocols include the subnet mask along with the IP address when advertising routing information.



Protocol                            Administrative distance
Directly connected route            0
Static route out an interface       1
Static route to next-hop address    1

Route Preference (Administrative distance) for different vendors
Protocol Cisco Mikrotik Juniper  Huawei (H3C), 3Com
Directly connected 0 0 0 0
Static 1* 1 5 60
OSPF internal 110 110 10 10
OSPF AS external 110 110 150 150
OSPF NSSA 110 110 150 150
IS-IS Level 1 internal 115 - 15 15
IS-IS Level 2 internal 115 - 18 15
IS-IS Level 1 external 115 - 160 15
IS-IS Level 2 external 115 - 165 15
RIPv1, RIPv2, RIPng 120 120 100 100
eBGP 20 20 170 255
iBGP 200 200 170 255
Unknown 255 - - 256
*Since IOS 12.2, the administrative distance of a static route with an exit interface is 1. Prior to the release of 12.2 it was in fact 0. Static route out an interface is recognized somewhere between 0 and 1. Static route out an interface is more trustworthy than Static route to next-hop address.


Neighbor Requirements for EIGRP and OSPF

Requirements EIGRP OSPF
Routers MUST be able to send/receive IP packets to one another YES YES
Interfaces MUST be in UP/UP state YES YES
Interfaces PRIMARY IP MUST be in SAME subnet YES YES
Interfaces MUST not be Passive on the connected interface YES YES
MUST pass authentication (if configured) YES YES



Router  IDs MUST be unique NO 1 YES
SAME  ASN  / Process ID YES NO
SAME  Hello / Dead intervals NO YES
SAME  MTU NO 2 YES
SAME  Area
SAME 'Stub' Area Flag
n/a
n/a
YES
YES
SAME  'K' Values YES n/a

1 - Duplicate EIGRP RIDs do not prevent routers from becoming neighbors, but it can cause problems when adding external EIGRP routes to the routing table.
2 - May allow the other router to be listed in the show ip ospf neighborcommand, but the MTU mismatch will prevent proper operation of the topology exchange 


Link Neighbor Requirements for EIGRP and OSPF 1
Link Neighbor Requirements for EIGRP and OSPF 2




Subnetting

Subnets Calculator  - http://jodies.de/ipcalc

192.168.5.63/28
a) bitmask  /28 =...240 :  32-28=4,    2^4=16  -> 256-16=240
b) range ..5.48-63    :  nets 5.0 , 5.16, 5.32, 5.48 (+16)
c) subnets 2^m =16  : blocksize - host bits = 8 - 4 =4
d) hosts     2^n -2 =14: 2^4-2 =14

My simple method for mask calculation:
1) dotted (long to short )
1.1) greater than /24 (>24)
      255.255.255.192 = /26
      1) 256-192 = 64
      2) 64 = 2^6
      3) 32 bit length - 6 bit = 26

1.2) less than /24 (>24)
      255.255.240.0 = /20
      0) last block .0 = minus 8 bits
      1) 256-240 =16
      2) 16 = 2^4
      3) 32 bit length - 4 bits - 8 bits = 20

2) CIDR (short to long)
2.1)  greater than /24 (>24)
        /27 = 255.255.255.224
       1) 32 - 27 = 5
       2) 2^5 = 32
       3) 256 - 32 = 224
2.2) les than /24 (<24)


For network (ISP)
1 users (/32) ~ 313 kbps (dec 2011)
1 users (/32) ~ 445 kbps (feb 2014, or +2.2 years)


CIDR Nr of /24 ~Traffic (mbps) Subnet Mask Addresses Wildcard Usable Addresses
/32 - 0.25 255.255.255.255 1 0.0.0.0 none
/31 -
255.255.255.254 2 0.0.0.1 none
/30 -
255.255.255.252 4 0.0.0.3 2
/29 -
255.255.255.248 8 0.0.0.7 6
/28 -
255.255.255.240 16 0.0.0.15 14
/27 -
255.255.255.224 32 0.0.0.31 30
/26 -
255.255.255.192 64 0.0.0.63 62
/25 -
255.255.255.128 128 0.0.0.127 126
/24 1 62.5 255.255.255.0 256 0.0.0.255 254
/23 2 125 255.255.254.0 512 0.0.1.255 510
/22 4 250 255.255.252.0 1 024 0.0.3.255 1 022
/21 8 500 255.255.248.0 2 048 0.0.7.255 2 046
/20 16 1000 (200) 255.255.240.0 4 096 0.0.15.255 4 094
/19 32 2000 255.255.224.0 8 192 0.0.31.255 8 190
/18 64 4000 255.255.192.0 16 384 0.0.63.255 16 382
/17 128 8000 255.255.128.0 32 768 0.0.127.255 32 766
/16 256 16000 255.255.0.0 65 536 0.0.255.255 65 534
/15 512 32000 255.254.0.0 131 072 0.1.255.255 131 070
/14 1024 64000 255.252.0.0 262 144 0.3.255.255 262 142
/13

255.248.0.0 524 288 0.7.255.255 524 286
/12

255.240.0.0 1 048 576 0.15.255.255 1 048 574
/11

255.224.0.0 2 097 152 0.31.255.255 2 097 150
/10

255.192.0.0 4 194 304 0.63.255.255 4 194 302
/9

255.128.0.0 8 388 608 0.127.255.255 8 388 606
/8

255.0.0.0 16 777 216 0.255.255.255 16 777 214
/7

254.0.0.0 33 554 432 1.255.255.255 33 554 430
/6

252.0.0.0 67 108 864 3.255.255.255 67 108 862
/5

248.0.0.0 134 217 728 7.255.255.255 134 217 726
/4

240.0.0.0 268 435 456 15.255.255.255 268 435 454
/3

224.0.0.0 536 870 912 31.255.255.255 536 879 910
/2

192.0.0.0 1 073 741 824 63.255.255.255 1 073 741 822
/1

128.0.0.0 2 147 483 648 127.255.255.255 2 147 483 646
/0

0.0.0.0 4 294 967 296 255.255.255.255 4 294 967 294

Decimal To Binary
Subnet Mask Wildcard
255 11111111 0 00000000
254 11111110 1 00000001
252 11111100 3 00000011
248 11111000 7 00000111
240 11110000 15 00001111
224 11100000 31 00011111
192 11000000 63 00111111
128 10000000 127 01111111
0 00000000 255 11111111

Classful Network Architecture
A 0.0.0.0 – 127.255.255.255
B 128.0.0.0 – 191.255.255.255
C 192.0.0.0 – 223.255.255.255
D 224.0.0.0 – 239.255.255.255
E 240.0.0.0 – 255.255.255.255

IANA-reserved private IPv4 network ranges

24-bit Block (/8 prefix, A) 10.0.0.0 – 10.255.255.255
20-bit Block (/12 prefix, B) 172.16.0.0 – 172.31.255.255
16-bit Block (/16 prefix, C) 192.168.0.0 – 192.168.255.255

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