CCIE RS – L2 WAN Circuit Technology – MLPPP

Multilink PPP

  • Provides load balancing functionality over multiple WAN links
  • RFC 1990
  • Allows packets to be fragmented and sent at same time over multiple p2p links

Link Fragmentation and Interleaving (LFI)

  • Type of Cisco QoS
  • Prevent small delay sensitive packets from having to wait on longer, delay insensitive packets to be completely serialized out an interface
  • Fragments larger packets
  • Ppp multilink interleave
  • Ppp multilink fragment-delay [#]

Configuration

Interface multilink [#]
Ip address
Ppp multilink
Ppp multilink group [#]

CCIE RS – Written – L2 – Implement and Troubleshoot VLANs

CCIE RS – Written – L2 – Implement and Troubleshoot VLANs

VLAN – Virtual LAN

  • Administratively defined subset of switch ports that are in the same broadcast domain
  • Broadcast domain – devices that can receive broadcast sent by another device
  • Best Practice – 1 to 1 relationship between IP subnet and VLAN

Configuration

  • Vlan [id]
  • Under interface > switchport access vlan [id]
  • Modify VLAN operational state (L2 only)
    • Can be suspended globaly for entire VTP or to local switch
    • Vlan [id] > state suspend (global) | shutdown (local)

Access Ports

Belongs and carries traffic for only 1 VLAN 

Configuration

interface > switchport access vlan [#]


VLAN Database

  • Vlan 0 – Reserved, not available for use
  • Vlan 1 – Default vlan for all access ports
    • Cannot be deleted or pruned
  • Vlan 4095 – Reserved, not available for use

Switch#sh vlan

VLAN Name                             Status    Ports
—- ——————————– ——— ——————————-
1    default                          active    Gi0/0, Gi0/1, Gi0/2
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup 

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
—- —– ———- —– —— —— ——– —- ——– —— ——
1    enet  100001     1500  –      –      –        –    –        0      0   
1002 fddi  101002     1500  –      –      –        –    –        0      0   
1003 tr    101003     1500  –      –      –        –    –        0      0   
1004 fdnet 101004     1500  –      –      –        ieee –        0      0   
1005 trnet 101005     1500  –      –      –        ibm  –        0      0   

Primary Secondary Type              Ports
——- ——— —————– ——————————————

Switch#


Normal VLAN

1 – 1001

  • Can be advertised with VTPv1 and 2
  • Configured in vlan database, global config
  • Details stored in vlan.dat
  • Can be pruned

1002 – 1005 Special uses

  • Cannot be pruned
  • 1002 fddi-default
  • 1003 token-ring-default
  • 1004 fddinet-default
  • 1005 trnet-default

Extended VLAN

1006 – 4094

VTPv1 and 2 must be in transparent mode


Voice VLAN

Enables access ports to carry traffic from an IP Phone

  • Portfast is automatically enabled when voice vlan is configured
    • Not disabled if voice vlan is removed

Configure how the Cisco IP Phone carries voice traffic:

  • vlan-id —Configure the phone to forward all voice traffic through the specified VLAN. By default, the Cisco IP Phone forwards the voice traffic with an IEEE 802.1Q priority of 5. Valid VLAN IDs are 1 to 4094.
  • dot1p —Configure the phone to use IEEE802.1p priority tagging for voice traffic and to use the default native VLAN (VLAN 0) to carry all traffic. By default, the Cisco IP Phone forwards the voice traffic with an IEEE 802.1p priority of 5.
  • none —Allow the phone to use its own configuration to send untagged voice traffic.
  • untagged —Configure the phone to send untagged voice traffic.

CCIE RS – Written – L2 – Implement and Troubleshoot Trunking

Implement and Troubleshoot Trunking


Trunking

  • Allows devices to send traffic for multiple vlans across a single link
  • Trunking protocols must match on both ends

ISL

  • Cisco Proprietary
  • Supports normal and extended vlans
  • Encapsulates original frame
    • 26 byte header + trailer for FCS
  • No concept of native vlan

802.1Q

  • Open Standard (IEEE)
  • Supports normal and extended vlans
  • Inserts tag into original frame
    • 4 byte header
    • Frame tagging
  • Concept of native vlan
    • Traffic in native vlan is untagged
    • All received untagged frames are sent over native vlan
    • Must match on both ends of trunk
    • Detection for mismatch
      • Cisco Switches – Proprietary extension in PVST+ and Rapid PVST+
      • CDP Neighbor can detect and report (syslog)
    • Default native vlan is 1
      • Best practice is to change to prevent vlan hopping attacks

DTP – Dynamic Trunking Protocol

  • Dynamically learn if device on other end wants to perform trunking and negotiate what protocol to use
  • Modes
    • Dynamic Auto – negotiate automatically
      • Prefers to be access port
    • Dynamic Desirable
      • Prefers to be a trunk port
      • Highest priority
      • Will choose ISL is both sides support
    • Different switch models have different default behaviors
    • DTP and VTP are independent
      • DTP carries the VTP domain name
  • Reduce number of vlans on trunk
    • Vlans must be configured on switch before being considered active
    • Administratively configure or use VTP pruning
      • Switchport trunk allowed [add | remove ]
  • Config
    • Switchport mode [trunk | dynanmic desirable / auto | access
    • Switchport nonegotiate
      • Port no longer sends DTP messages
    • Switchport trunk encapsulation [isl | dot1q]

Q in Q Tunneling

  • VLANs traditionally do not extend past WAN boundary
  • Standard 802.1ad – Provider Bridges
  • Allow SP to preserve 802.1q vlan tag across WAN service
  • CDP and VTP can be configured to pass transparently over Q-in-Q
  • New tagging concept
    • C-Tag – Original customer tagged frame
    • S-Tag – Additional tag added to C-Tag frame at ingress of SP
      • Tag is removed at egress of SP, preserving original C-Tag
      • Different customers get different S-Tags
  • Configuration
    • Change MTU to 1504 for extra header size

Manual VLAN Pruning

Manually specify which vlans are allowed across a trunk link


VTP – VLAN Trunking Protocol

  • Advertises vlan config information to neighboring switches
  • Allows vlan config to be done from 1 switch in the domain (dynamic)
  • Advertises VLAN ID, name and type
  • Does not forward which ports are in the vlan
  • Sends updates out all active trunk links by default
    • Without domain name switches do not send any VTP updates
  • VTP starts working when there is an active trunk link and domain name
  • Configuration
    • Vtp domain [name]
    • Show vtp status
    • Options
      • Domain – sets domain name
        • Switch can only belogn to one domain
      • Password – sets password to prevent unauthorized switches from joining domain
      • Mode [server | client | transparent]
      • Version [1 | 2 | 3]
        • Can configure on server switch and will sync with other switches
        • V3 must be manually configured and have domain name configured
      • Pruning
        • Prevent flooding per-VLAN to switches that do not have the VLAN configured
        • Only applied to normal VLAN range
      • Interface
        • Sets interface whos IP is used to ID the switch
        • Default is to use IP of lowest numbered SVI

VTPv1

Version 1 is default

  • Supports only normal vlan range

Message Types (v1 and v2)

  • Summary advertise
    • Originated by VTP server and client every 5 minutes and after each modification to vlan database
    • Carries domain name, revision number, ID of updater, timestamp, MD5, password & number of subset advertise
    • Does not carry vlan database contents
  • Subset Advertise
    • Originated by server and client after modification of vlan database
    • Carries full vlan database contents
  • Advertise Request
    • Request neighbors complete vlan database or part of it
    • Request sent when switch enters client mode or client switch is restarted
  • Join
    • Every 6 seconds if VTP pruning is active

Update Process (v1 and v2)

  • Begins when a modification is made on a vlan
  • VTP server will increment revision number by 1 and advertise entire vlan database with new revision number
  • Revision number allow switches to know when vlan database changes have occurred
    • Switches replace their vlan database when a larger revision shows up

VTP Modes

  • Server –
    • Default with no domain name
    • Updates to not occur until a domain name is configured
  • Client
    • Will assume first received domain name
    • Default domain is NULL
  • Transparent / Off
    • Prevents switches from listening to other switches VTP updates
  • Protect VTP domain – VTP password
    • Summary adv – carries MD5 hash computed over the vlan database contents and VTP password if configured

VTPv2

Enhanced version of v1

  • Supports token ring concentrator relay function and bridge relay function
    • Not used in ethernet based networks
  • Supports unknown TLV (Type Length Value)
    • V1 would drop unrecognized TLV’s which would stop propagation to other switches
  • Optimized vlan database consistency checking
    • Implementation optimization
    • Skips consistency check if change was received by a VTP message

VTPv3

Introduced to IOS release 12.2(52)SE

  • New server roles – Addresses problem of inadvertent rewrites to the vlan database
    • Primary – Only 1 at a time
      • Can modify VTP domain contents
      • Only switch who’s vlan database is propagated through domain
      • Database will be shared if switch agrees on domain name and ID of primary server (MAC address)
    • Secondary –
      • Cannot make changes,
      • but can be promoted
      • All other server switches in domain are secondary
    • Primary role is a runtime state. Does not get saved into configuration
    • Server role helps prevent unwanted changes to VTP domain
  • Password storage and usage improved
    • Encrypted and cannot be displayed in plaintext
    • Promotion of secondary required entering password in plaintext
    • String is carried encrypted to different switches
  • Capable of distributing full range of vlans and private vlans
    • No longer need to be in transparent mode when using extended vlan range and private vlans
    • Pruning only applied to normal vlan range
  • Supports VTP off
    • Switch does not participate in VTP and drops all VTP messages
  • Distributes content of MST region config
  • Client switches cannot make changes to domain or be promoted
  • Both Secondary and Client store copy of primaries vlan database and share with neighboring server and client if they agree on the primaries ID
  • Secondary or client servers with higher revision number can overwrite vlan database, but must match on domain name, primary ID and password
  • Conflicts
    • Server or client in domain having different primary server IDs
    • Conflciting switches do not sync the vlan database even if all other parameters match
  • Promotion to primary sever done in exec mode
    • Vtp primary
  • Cannot reset revision number to 0 by switching mode to transparent
    • Only will be reset by modifying the domain name or configuring password
  • Switches that cannot run v3, the port will revert to v2
    • V3 to v1 is not supported

VTP Pruning

Reduces unnecessary flooded traffic such as broadcasts, multicast and unicast packet

  • Disabled by default
  • Enabling on server enables for entire domain
  • Vlans 2 – 1000 are eligible for pruning
  • Cmd: vtp pruning