Saturday, January 2, 2010

Frame Relay Part 3: interface types

Third part of my frame-relay tour, here we will talk about interface types.

Topology still unchanged from the previous parts, here the picture:



There are several interface types on frame-relay, according on how you configure your serial interface and on what is the purpose you will archive:

1) physical interface
2) subinterface multipoint
3) subinterface point-to-point

Let's talk about each type..

1) Physical interfaces
-are threated as multipoint
-all DLCIs declared by lmi are assigned to physical interfaces
From a L3 point of view, all the neighbors are expected in the same subnet and you can use a static L3 to L2 mapping or inverse arp, as previously seen.
Note also that by default, on frame-relay physical interfaces the SPLIT ORIZON is disabled, useful to solve distance-vector routing protocol issues.

Example:
R4#sh run int ser 0/3/0 | beg int
interface Serial0/3/0
description R4 - (R1|R2) without intverse-arp
ip address 10.0.0.4 255.255.255.0
encapsulation frame-relay
frame-relay map ip 10.0.0.2 402 broadcast
frame-relay map ip 10.0.0.1 401 broadcast
no frame-relay inverse-arp
end

R4#sh frame-relay map
Serial0/3/0 (up): ip 10.0.0.1 dlci 401(0x191,0x6410), static,
broadcast,
CISCO, status defined, active
Serial0/3/0 (up): ip 10.0.0.2 dlci 402(0x192,0x6420), static,
broadcast,
CISCO, status defined, active

R4#show ip interface ser 0/3/0
Serial0/3/0 is up, line protocol is up
Internet address is 10.0.0.4/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Local Proxy ARP is disabled
Security level is default
Split horizon is disabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is enabled
IP fast switching on the same interface is enabled
IP Flow switching is disabled
IP CEF switching is enabled
IP CEF switching turbo vector
IP multicast fast switching is enabled
IP multicast distributed fast switching is disabled
IP route-cache flags are Fast, CEF
Router Discovery is disabled
IP output packet accounting is disabled
IP access violation accounting is disabled
TCP/IP header compression is disabled
RTP/IP header compression is disabled
Policy routing is disabled
Network address translation is disabled
BGP Policy Mapping is disabled
Input features: MCI Check
WCCP Redirect outbound is disabled
WCCP Redirect inbound is disabled
WCCP Redirect exclude is disabled



Subinterfaces Multipoint
-DLCIs must manually assigned to the subinterface if inverse arp is used
-ip/ipv6 must be manually mapped if inverse arp is disabled
With subinterfaces multipoint, split orizon is enabled by default, as shown in the following example:

R4#sh run int ser 0/3/0.1  | beg int
interface Serial0/3/0.1 multipoint
description R4 - (R1|R2) with inverse-arp
ip address 10.0.0.4 255.255.255.0
snmp trap link-status
frame-relay interface-dlci 401
frame-relay interface-dlci 402
end

R4#sh frame-relay pvc | inc DLCI
DLCI = 401, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/3/0.1
DLCI = 402, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/3/0.1
DLCI = 403, DLCI USAGE = UNUSED, PVC STATUS = ACTIVE, INTERFACE = Serial0/3/0

R4#sh ip interface serial 0/3/0.1
Serial0/3/0.1 is up, line protocol is up
Internet address is 10.0.0.4/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Local Proxy ARP is disabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is enabled
IP fast switching on the same interface is enabled
IP Flow switching is disabled
IP CEF switching is enabled
IP CEF switching turbo vector
IP multicast fast switching is enabled
IP multicast distributed fast switching is disabled
IP route-cache flags are Fast, CEF
Router Discovery is disabled
IP output packet accounting is disabled
IP access violation accounting is disabled
TCP/IP header compression is disabled
RTP/IP header compression is disabled
Policy routing is disabled
Network address translation is disabled
BGP Policy Mapping is disabled
Input features: MCI Check
WCCP Redirect outbound is disabled
WCCP Redirect inbound is disabled
WCCP Redirect exclude is disabled
R4#



Subinterfaces Point-to-point
-a single DLCI can be specified with the "frame-relay interface-dlci " command
-don't send out inverse-arp queries, but still respond to the received inarp queries.
This type of interface assumes that the whole subnet is reachable through the only DLCI, so no need of L3 to L2 resolution and it's nice to have Split Orizon enabled for distance-vector routing protocols (otherwise you will maybe have routing l00ps)

Example:
R2#sh run | beg Serial0/2/0
interface Serial0/2/0:1
no ip address
encapsulation frame-relay
!
interface Serial0/2/0:1.1 point-to-point
description R2 - R4
ip address 10.0.0.2 255.255.255.0
snmp trap link-status
frame-relay interface-dlci 204
!
interface Serial0/2/0:1.2 point-to-point
description R2 - R3
ip address 10.0.1.2 255.255.255.0
snmp trap link-status
frame-relay interface-dlci 203

R2#sh frame-relay map
Serial0/2/0:1.2 (up): point-to-point dlci, dlci 203(0xCB,0x30B0), broadcast
status defined, active
Serial0/2/0:1.1 (up): point-to-point dlci, dlci 204(0xCC,0x30C0), broadcast
status defined, active

R2#sh ip interface ser 0/2/0:1.2
Serial0/2/0:1.2 is up, line protocol is up
Internet address is 10.0.1.2/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Local Proxy ARP is disabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is enabled
IP fast switching on the same interface is enabled
IP Flow switching is disabled
IP CEF switching is enabled
IP CEF switching turbo vector
IP Null turbo vector
IP multicast fast switching is enabled
IP multicast distributed fast switching is disabled
IP route-cache flags are Fast, CEF
Router Discovery is disabled
IP output packet accounting is disabled
IP access violation accounting is disabled
TCP/IP header compression is disabled
RTP/IP header compression is disabled
Policy routing is disabled
Network address translation is disabled
BGP Policy Mapping is disabled
Input features: MCI Check
WCCP Redirect outbound is disabled
WCCP Redirect inbound is disabled
WCCP Redirect exclude is disabled


!-- END of part 3: next part will hopefully follow soon, with dirty tricks and routing examples

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