Reference: Special addresses

This page serves as a refererence guide for special addresses used in networking.

MAC Addresses

PatternPurposeUsage
00:00:0C:07:AC:[XX]HSRP v1 IPv4Last two nibbles are the HSRP group
00:00:0C:9F:F[X:XX]HSRP v2 IPv4Last three nibbles are the HSRP Group
00:05:73:A0:0[X:XX]HSRP v2 IPv6Last three nibbles are the HSRP Group
00:00:5E:00:01:[XX]VRRP IPv4Last two nibbles are the Virtual Router ID
00:00:5E:00:02:[XX]VRRP IPv6Last two nibbles are the Virtual Router ID
00:07:B4:00:[XX]:[YY]GLBPLast octet is GLBP group [XX] followed by the AVF number [YY]
00:23:04:EE:BE:[XX]VPC System-macLast two nibbles is the VPC Domain ID
01:80:C2:00:00:00STP BPDUDestination MAC for BPDUs
01:00:0C:CC:CC:CDCisco PVSTP BPDUDestination MAC for BPDUs
01:80:C2:00:00:02IEEE Std 802.3 Slow Protocols multicast addressUsed for LACP etc
01:00:0C:CC:CC:CCMulticast MAC for Cisco servicesUsed for PAgP/CDP/VTP

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Reference: Higher or lower preferred?

This will be a dynamic document to document all the scenarios where it’s not clear which is better; A higher value or a lower value?

I have noticed that as a general rule; For layer 2 technologies a lower value is preferred and for layer 3 a higher value is prefered. The purpose of this post is to keep a list so I can see if this rule holds out or is proven wrong on some occasions.

Cisco

ValueDefault ValuePreferred value
HSRP Priority100Higher
BGP Local-preference100Higher
BGP Weight (Cisco)0Higher
BGP MED0Lower
Spanning-tree bridge ID32768Lower
Router ID auto selectionIP Address1Higher

1The highest active configured IP on a loopback is preferred. If there are no lookbacks then the highest IP address on an active interface is chosen next.

Palo Alto

ValueDefault ValuePreferred value
HA Device Priority100Lower2

2The palo alto documentation covers this is a very confusing manner. It states that the device with the highest device priority is chosen as the active. It goes on to say that a lower integer value means the device has a higher priority.

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Reference: Networking Mnemonics

The following is a list of networking Mnemonics which I have either created, been told about or read about as a method of remembering various aspects of networking as part of my study. This list will be updated as time goes on:

The OSI Model

OSI LayerMnemonicOSI Layer description
1PeoplePresentation
2Don’tData-link
3NeedNetwork
4ThoseTransport
5StupidSession
6PacketsPresentation
7AnywayApplication

The OSI Model (Alternative)
Please Do Not Take Sales Peoples Advice

EIGRP K Values

K ValueMnemonicK Value Description
K1BigBandwidth
K2LatenciesLoad
K3Don’tDelay
K4ReallyReliability
K5MatterMTU

OSPF LSA Types

LSA TypeMnemonicLSA Description
Type 1RightRouter LSA
Type 2NowNetwork LSA
Type 3SomeSummary LSA
Type 4ArgueASBR Summary LSA
Type 5As1ASBR External LSA
Type 6GoodGroup Membership LSA
Type 7NetworkNSSA LSA
Type 8EngineersExternal Attributes
Type 9LookLink Scope Opaque
Type 10AlwaysArea Scope Opaque
Type 11AsideAS Scope Opaque

1 Think of As path to remember external

Cisco BGP Attributes (NB: Not yet completed)

BGP Metric Mneumonic PreferenceSignificanceRequirement
WeightHighestLocal
Local PreferenceHighestLocal AS
Local originatedLocal originatedLocal
AS PathShortestGlobal
MEDLowerGlobal
ExternaleBGP > iBGP
IGP costLowest
eBGP PeerinOldest
Router IDLowest

BGP attributes are evaluated from the top down. Preference is which value is better than another value and significance is whether that property carries to other AS, Is local to the AS or is local to the device. Compatibility is whether something is vendor proprietarty.

Syslog Severity levels

Syslog levelMneumonicSyslog Level description
0EveryoneEmergency
1AlwaysAlert
2ComplainsCritical
3EvenError
4WhenWarning
5NothingNotification
6IsInformational
7DifferentDebugging

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