Minor Stack Protocol Version Number Incompatibility Among Stack-Capable Switches

Minor Stack Protocol Version Number Incompatibility Among Stack-Capable Switches


Switches with the same major version number but with a different minor version number are considered partially compatible. When connected to a switch stack, a partially compatible switch enters version-mismatch (VM) mode and cannot join the stack as a fully functioning member. The software detects the mismatched software and tries to upgrade (or downgrade) the switch in VM mode with the switch stack image or with a tar file image from the switch stack flash memory. The software uses the automatic upgrade (auto-upgrade) and the automatic advise (auto-advise) features.

The port LEDs on switches in version-mismatch mode will also remain off. Pressing the Mode button does not change the LED mode.

OSPFv2 and OSPFv3 headers

#DoYouKnow #OSFP #Routing

All OSPFv2 packets have a common 24-byte header, and OSPFv3 packets have a common 16-byte header, that contains all information necessary to determine whether OSPF should accept the packet. The header consists of the following fields:

• Version number—The current OSPF version number. This can be either 2 or 3.
• Type—Type of OSPF packet.
• Packet length—Length of the packet, in bytes, including the header.
• Router ID—IP address of the router from which the packet originated.
• Area ID—Identifier of the area in which the packet is traveling. Each OSPF packet is associated with a single area. Packets traveling over a virtual link are labeled with the backbone area ID, 0.0.0.0. .
• Checksum—Fletcher checksum.
• Authentication—(OSPFv2 only) Authentication scheme and authentication information.
• Instance ID—(OSPFv3 only) Identifier used when there are multiple OSPFv3 realms configured on a link.

Cisco router load balancing and CEF (Cisco Express Forwarding)

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Per-destination or per-packet load-balancing depends on the type of switching scheme used for IP packets. By default, on most Cisco routers, fast switching is enabled under interfaces. This is a demand caching scheme that does per-destination load-balancing. To set per-packet load-balancing, enable process switching (or disable fast switching), use these commands:

Router(config-if)# no ip route-cache

Now the router CPU looks at every single packet and load balances on the number of routes in the routing table for the destination. This can crash a low-end router because the CPU must do all the processing.

Newer switching schemes such as Cisco Express Forwarding (CEF) allow you to do per-packet and per-destination load-balancing more quickly. However, it does imply that you have the extra resources to deal with maintaining CEF entries and adjacencies.

When you work with CEF, you could ask: Who does the load balancing, CEF or the routing protocol used? The way in which CEF works is that CEF does the switching of the packet based on the routing table which is being populated by the routing protocols.

I like cef...

#Extra tips for my blog readers:

, CEF performs the load-balancing once the routing protocol table is calculated.

Block "Botnet and Control & Command Servers" on Fortigate

Are you making same "big" mistake in Fortigate firewall configuration?  Are you blocking "Botnet & C&C Servers"? He (My friend, Security Implementation Engineer) is unaware or ignoring about configuration changes onward Forti OS 5.4. This is called "Scan Outgoing Connections to Botnet Sites".  Previously it was (5.2)  "Detect Connections to Botnet C&C Servers" in Security Profiles -> AntiVirus. but today this is available "Scan Outgoing Connections to Botnet Sites"  in Network->Interfaces->Edit Interface (WAN).  #securities #Fortigate #fortinet #securityawareness #DoYouKnow

Multicast OSPF LSA (Type 6) on Cisco router

Cisco routers do not support LSA Type 6 Multicast OSPF (MOSPF), and they generate syslog messages if they receive such packets. If the router is receiving many MOSPF packets, you might want to configure the router to ignore the packets and thus prevent a large number of syslog messages.


Commands:
#Router ospf 0.0.0.1
#ignore lsa mospf

Does ospf having backup path?

 OSPF uses the SPF algorithm. The information contained in a router’s OSPF link state database is the “MAP” that is used to calculate the best path to a remote network. However, unlike EIGRP, OSPF does not keep backup paths to routes, rather, when a route to a network goes down, the SPF algorithm is run again to determine a backup or alternate path.
Keep in mind no backup link.. if there are any dual active paths to any destination with same metric then load balancing will work (default up to 4 Path).

What Do We Mean by Link-States?

What Do We Mean by Link-States?

OSPF is a link-state protocol. We could think of a link as being an interface on the router. The state of the link is a description of that interface and of its relationship to its neighboring routers. A description of the interface would include, for example, the IP address of the interface, the mask, the type of network it is connected to, the routers connected to that network and so on. The collection of all these link-states would form a link-state database.

OSPF LSA in Details

Somedays before (last year), I have published a post about the OSPF LSAs types and definitions. Today I am going to share some more details about the SLAs as which router will generate the which LSAs:

1. 

SLA Name: Router LSA 

Link-State ID: Originating router ID of the router

Generated By: Router LSAs are generated by every router. 

2. 

SLA Name: Network LSA 

Link-State ID: Interface IP address of the DR

Generated By: Network LSAs are generated by the DR on a multi-access segment. They are the representation of the multi-access segment and all the routers attached to the segment. Segments that do not have a DR, such as point-to-point, will not have a network LSA.

3.

SLA Name: Network summary LSA

Link-State ID: Destination network number

Generated By: Network summary LSAs are generated by ABRs. 

4.

SLA Name: ASBR summary LSA

Link-State ID: Router ID of AS boundary router

Generated By: ASBR summary LSAs are also generated by the ABR. This LSA describes the location of an ASBR, not a network. 

5. 

SLA Name: AS external LSA

Link-State ID: External network number

Generated By: Autonomous System (AS) External LSAs are originated by the ASBRs and describe a network outside of the AS.

7. 

SLA Name: NSSA external LSA
Link-State ID: External network number
Generated By: Not-So-Stubby Area (NSSA) external LSAs are originated by the ASBR within the NSSA. These types of LSAs are flooded only throughout the NSSA.

I hope it will very helpful for you!

OSPF Tips - Summarization of Network

#CiscoTips #OSPF #DoYouKnow

An internal summary route is generated if at least one subnet within the area falls in the summary address range and the summarized route metric is equal to the lowest cost of all the subnets within the summary address range. Interarea summarization can only be done for the intra-area routes of connected areas, and the ABR creates a route to Null0 to avoid loops in the absence of more specific routes.

OSPF network planning tips - Summarization of network

#CiscoTips #DoYouKnow #OSPF #Design Summarization design is a process of network planning: One step fails, Network fail::: If the OSPF design includes many ABRs or ASBRs, suboptimal routing is possible. This is one of the drawbacks of summarization. Route summarization requires a good addressing plan—an assignment of subnets and addresses that are based on the OSPF area structure and lends itself to aggregation at the OSPF area borders.