Frame-Relay - Basics - Part1

Understanding Frame-relay basics;

What happens when you encapsulate an Interface with frame-relay
What's the effect running frame-relay on;
- the main-interface

Typical config on the main interface;

R1#sh run int s1/0

Building configuration...

Current configuration : 158 bytes

interface Serial1/0

ip address 155.1.1.1 255.255.255.0

encapsulation frame-relay

serial restart-delay 0

frame-relay map ip 155.1.1.5 105 broadcast

end

a point-to-point sub-interface

Typical config on the sub-interface;

R2#sh run int s1/0.205

Building configuration...

Current configuration : 118 bytes

interface Serial1/0.205 point-to-point

ip address 155.1.25.2 255.255.255.0

frame-relay interface-dlci 205

end

When configuring FR on a p2p sub-interface all you need to assign is the DLCI it needs to use. There is no L3 to L2 mapping required. For a p2p sub-interface there is only one point of exit to the rest of the network.

a multipoint sub-interface

Checking if Frame-Relay is running
- show commands
- Frame-Relay types
Why does Frame-Relay use Inverse ARP

The same way Ethernet uses ARP to find the MAC address associated with an IP address, in FR Inverse ARP is used to find a IP address connected to a local Layer 2 circuit - i.e. DLCI number.

When you un-shut an interface configured to run FR (i.e.encap frame-realy), the interface status using "show ip int brief" would show interface as up/up.

When you un-shut an interface running FR and it the interface show as up/down that mean there is something wrong with the FR switch and LMI is not working.
Serial1/0 unassigned YES manual up down
Because FR is local to the router and the FR-switch. This interface status does not tell you anything about the router you're trying to connect to.

Effects of not running Inverse ARP

Inverse ARP is running automatically on an interface configured to run FR. Inverse ARP is process mapping the L2 circuit (DLCI) to a L3 IP address. When you configure a static map on the FR interface Inverse ARP is disabled automatically.

interface Serial1/0
ip address 155.1.1.5 255.255.255.0
encapsulation frame-relay
serial restart-delay 0
frame-relay map ip 155.1.1.1 501 broadcast
end

*********************

R5#sh frame-relay map

Serial1/0 (up): ip 155.1.1.1 dlci 501(0x1F5,0x7C50), static,

broadcast,

CISCO, status defined, active

You can disable Inverse ARP per DLCI on the interface sub-command or if you don't specify any protocol or DLCI; Inverse ARP will be disabled for all protocols and DLCIs;

i.e.

R5(config-if)#no frame-relay inverse-arp [protocol]
or
R5(config-if)#no frame-relay inverse-arp
*************************************

OSPF Review

Network type Point-to-Point

OSPF network point-to-point is the default option for point-to-point interfaces such as HDLC, PPP, or point-to-point NBMA subinterfaces. It uses multicast hellos, does not use the DR/BDR election, and only supports the adjacency of exactly two neighbors on a segment. No special design considerations need to be taken into account for point-to-point OSPF interfaces
To note;

Unicats Hellos

Network type Point-to-Multipoint

OSPF network type point-to-multipoint is specifically designed to solve

reachability problems in partially meshed NBMA network designs. Unlike network

type point-to-point, it sends hellos as multicasts. And does not support the

DR/BDR election. Unlike point-to-point however, multiple adjacencies on a

single interface are supported.
To note;

Multicast Hellos to 224.0.0.5
In a Hub-Spoke design
- Hub - needs mapping to all spokes with BROADCAST key word - to enable reachability to all the spokes
- Spoke - needs a map ONLY to the HUB with BROADCAST key word - to enable reachability to all the spokes via the HUB.

Network type Point-to-Multipoint Non-Broadcast

OSPF network type point-to-multipoint non-broadcast is essentially the same as
network type point-to-multipoint, with one exception. Point-to-multipoint network
type uses multicast hellos, while point-to-multipoint non-broadcast uses unicast
hellos. Both do not support the DR/BDR election.

OSPF Basics

OSPF Route decision Process

Regardless of the metric or distance OSPF would prefer;

O – Intra-Area routes

OIA – Inter-Area route

E1 – External 1

E2 – External 2

N1 – NSSA type 1

N2 – NSSA type 2

E1 vs E2

E1 adds the metric every hop. E2 however, does not increment the metric when populating the routing table (this is the seed Metric). But routing decisions are made for equal metric exit points using the “forward Metric”

OSPF Area Types

Stub Area

VLAN Trunking Protocol (VTP)

VTP Part 1

Pruning:

Pruning eligible list :- VLANs that are assigned in the pruning eligible list are "eligible" to be pruned. i.e. you're saying, prune (or remove) VLANs that NOT requested by other switches when trunked.
When you remove a VLAN from the "prune eligible" list, you're saying that VLAN(s) should not be pruned. i.e. the VLAN(s) are to be present on the trunk all the time.

Configuration:
You configure this on the trunk ports on a L2/3 switch;
SW1(config)#int range g1/0/13 - 21
SW1(config-if-range)#switchport trunk pruning vlan 2-6,8-1001
The second line adds VLANs 2-1001 in the prune eligible list except VLAN 7.

Verification
SW1#sh int trunk | in pruned
Port        Vlans in spanning tree forwarding state and not pruned
SW1#sh int trunk | b pruned
Port        Vlans in spanning tree forwarding state and not pruned
Gi1/0/13    1,5,7-10,22,43,58,67,79,146
Gi1/0/14    1,7
Gi1/0/15    1,7
Gi1/0/16    5,9,43,79
Gi1/0/17    none
Gi1/0/18    none
Gi1/0/19    1,10,146
Gi1/0/20    none
Gi1/0/21    none

Variations of pruning:

SW1(config-if-range)#switchport trunk pruning vlan ?
WORD    VLAN IDs of the allowed VLANs when this port is in trunking mode
add     add VLANs to the current list
except all VLANs except the following
none    no VLANs
remove remove VLANs from the current list

BGP Review

Local Preference
Local-Pref is used to influence out-bound traffic from your AS; you apply it to in-bound route(s) (i.e. BGP neighbour interface).

Therefore, you apply LP to an INBOUND ROUTE to influence OUTBOUND TRAFFIC

MED/AS-path Prepend

MED/AS-Path Prepend is used to influence in-bound traffic to a AS, you apply it to the out-bound route (i.e. BGP neighbour interface).

Therefore, you apply LP to an OUTBOUND ROUTE to influence INBOUND TRAFFIC

Network Warrior

Sunday, October 13, 2013

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