3 types of OSPF authentication

These are the three different types of authentication supported by OSPF.

Null Authentication—This is also called Type 0 and it means no authentication information is included in the packet header. It is the default.

Plain Text Authentication—This is also called Type 1 and it uses simple clear-text passwords.

MD5 Authentication—This is also called Type 2 and it uses MD5 cryptographic passwords.

Authentication does not need to be set. However, if it is set, all peer routers on the same segment must have the same password and authentication method. The examples in this document demonstrate configurations for both plain text and MD5 authentication.

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Example Spanning-Tree Port Priority vs. Cost

from: http://www.cciecandidate.com/?p=585

I started responding to Nkl Hd ’s question, but realized it may be a little bit long-winded for a response.

Consider this example:
SW1-int g0/7 –> SW2-int F0/7
SW1-int g0/8 –> SW2-int F0/8

Root SW – SW1 for vlan 199
SW1(config)#spanning-tree vlan 199 root primary

SW1 – All ports in VLAN designated and forwarding because switch is root
##################################
SW1#sho spanning-tree int g0/7

Vlan Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
VLAN0001 Root FWD 19 128.7 P2p
VLAN0199 Desg FWD 19 128.7 P2p
SW1#sho spanning-tree int g0/8

Vlan Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
VLAN0001 Altn BLK 19 128.8 P2p
VLAN0199 Desg FWD 19 128.8 P2p
#################################

SW2
##################################
SW2#sho spanning-tree int f0/7

Vlan Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
VLAN0001 Desg FWD 19 128.7 P2p
VLAN0199 Root FWD 19 128.7 P2p
SW2#sho spanning-tree int f0/8

Vlan Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
VLAN0001 Desg FWD 19 128.8 P2p
VLAN0199 Altn BLK 19 128.8 P2p
##################################
int f0/7 is root switch and forwarding because cost is equal

PORT-PRIORITY

Port priority is utilized in this instance, but it’s the port priority on SW1 that is used (upstream) – the lower value is preferred

So, to move port SW2-f0/8 into a forwarding state you will change the port priority on one of SW1’s interfaces – REMEMBER, lowest value on the upstream (SW1) is utilized by SW2 to pick the root port

Default port priority is 128 & port # – you may change this in increments of 16
**Also remember to wait for topology change – you won’t see it immediately (forward delay timer X 2 15×2=30sec by default)**

SW1 – we can change the port priority on interface g0/7 OR g0/8 to influence this decision
OPTION 1 – You’re asked to change the config on port g0/7 – make the priority larger than 128
OPTION 2 – You’re asked to change the config on port g0/8 – make the priority lower than 128
OPTION 1 (priority)
############################################

SW1(config)#int g0/7
SW1(config-if)#spanning-tree port-priority ?
port priority in increments of 16
SW1(config-if)#spanning-tree port-priority 240
####################################

Notice, now F0/8 is the root port (forwarding)
####################################
SW2#sho spanning-tree int f0/7

Vlan Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
VLAN0001 Desg FWD 19 128.7 P2p
VLAN0199 Altn BLK 19 128.7 P2p
SW2#sho spanning-tree int f0/8

Vlan Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
VLAN0001 Desg FWD 19 128.8 P2p
VLAN0199 Root FWD 19 128.8 P2p
####################################

OPTION 2(priority)
####################################
SW1(config)#int g0/8
SW1(config-if)#spanning-tree port-priority ?
port priority in increments of 16

SW1(config-if)#spanning-tree port-priority 0
####################################
Notice, now F0/8 is the root port (forwarding)
####################################
SW2#sho spanning-tree int f0/7

Vlan Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
VLAN0001 Desg FWD 19 128.7 P2p
VLAN0199 Altn BLK 19 128.7 P2p
SW2#sho spanning-tree int f0/8

Vlan Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
VLAN0001 Desg FWD 19 128.8 P2p
VLAN0199 Root FWD 19 128.8 P2p
####################################

COST

Before any changes are made, check the topology

####################################

SW2#sho spanning-tree vlan 199 | beg Interface
Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Fa0/7 Root FWD 19 128.7 P2p
Fa0/8 Altn BLK 19 128.8 P2p

####################################

notice that path cost on both interfaces is equal (19) – so, as above there are 2 options

OPTION 1 – You’re asked to change the config on port SW2 f0/7 – make the cost higher than 19
OPTION 2 – You’re asked to change the config on port SW2 f0/8 – make the cost lower than 19

Option 1 (cost)
####################################
SW2(config)#int f0/7
SW2(config-if)#spanning-tree cost 21
####################################

####################################
SW2#sho spanning-tree vlan 199 | beg Interface
Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Fa0/7 Altn BLK 21 128.7 P2p
Fa0/8 Root FWD 19 128.8 P2p
####################################

Option 2 (cost)
####################################
SW2(config)#int f0/8
SW2(config-if)#spanning-tree cost 18
####################################

####################################
SW2#sho spanning-tree vlan 199 | beg Interface
Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Fa0/7 Altn BLK 19 128.7 P2p
Fa0/8 Root FWD 18 128.8 P2p
####################################

This can also be used for MST, the interface command is then SW2(config-if)# spanning-tree mst instance# [cost | port-priority]

Hopefully this clears things up a bit.

EIGRP Packet types – multicast and unicast

EIGRP uses five packet types:

Hello/Acks

Updates

Queries

Replies

Requests

As stated earlier, hellos are multicast for neighbor discovery/recovery. They do not require acknowledgment. A hello with no data is also used as an acknowledgment (ack). Acks are always sent using a unicast address and contain a non-zero acknowledgment number.

Updates are used to convey reachability of destinations. When a new neighbor is discovered, update packets are sent so the neighbor can build up its topology table. In this case, update packets are unicast. In other cases, such as a link cost change, updates are multicast. Updates are always transmitted reliably.

Queries and replies are sent when destinations go into Active state. Queries are always multicast unless they are sent in response to a received query. In this case, it is unicast back to the successor that originated the query. Replies are always sent in response to queries to indicate to the originator that it does not need to go into Active state because it has feasible successors. Replies are unicast to the originator of the query. Both queries and replies are transmitted reliably.

Request packets are used to get specific information from one or more neighbors. Request packets are used in route server applications. They can be multicast or unicast. Requests are transmitted unreliably.