Frame Relay現在越來越不流行了,不過在過去的設計中被廣泛應用。
所以工作上還是能經常見到的, 這篇博文從二層簡單總結下FR的一些概念
在介紹Frame Relay之前,先了解下廣播介質和非廣播介質的區別:
Broadcast Media (廣播介質): Ethernet 、 Token-Ring、FDDI
特點:
- 源可以同時向所有連接(二層)目的地址通話
- 簡化了三層到二層的解析
Non-Broadcast Multi Access (NBMA): Frame Relay、ISDN、ATM etc。
特點:
- 源不能同時和二層相連的所有目的地址通話
- 三層的廣播通過二層重複的單播實現 (pseudo-broadcast)
========三層到二層的地址解析對比=======
廣播介質的三層地址解析:遠程二層MAC地址和遠程三層地址綁定
- IPv4 Adress Resolution Protocol ( ARP)
- 廣播請求 - 誰知道1.1.1.1的MAC地址
- 單播回覆 - 我的MAC是abcd.abcd.abcd
廣播介質的三層地址解析:遠程或本地的二層MAC地址和遠程三層地址綁定
- 本地FR DLCI和遠程IPv4地址綁定
- 遠端ISDN電話和原電IPX地址綁定
- 反向ARP用解析遠程三層地址到本地二層地址
- 只有直接相連的設備可以進行解析
NBMA 端口類型:
多點接口 - 可連接多個二層鏈路 & 需要三層到二層的解析 (FR & ATM main interface)
單點接口 - 連接一個二層鏈路 & 不需要三層到二層解析 (PPP link, FR p2p subinterface)
======================================
1. FR 簡介
應用了NBMA - 也就意味着潛在存在三層到二層解析問題
DLCI - Data link Connection Identifier (數字鏈路識別碼)
- 二層尋址
- DLCI本地有效
LMI - Local Management Interface
- DTE or DCE 通訊
- 彙報虛擬鏈路的狀態
- 動態解析通過反向ARP請求 (inverse ARP)
- 靜態解析通過命令frame-relay map
- 反向APR請求發送可以disable - no frame-relay inverse arp [protocol] [dlci]
- 回覆不能被disable (這是個潛在的問題)
- frame-relay map [protocol] [address] dlci [broadcast]
- 和靜態ARP的邏輯一樣
- 偵測封裝
- 通過DLCI學習LMI
- 給所有DLCIs發送BOOTP
- 如果請求失敗了,會自動配置0.0.0.0 mapping
- 這可能破壞之後的路由配置
- 解決方法就是save config and reload
An interface is by default a "multipoint" interface so, frame-relay inverse-arp is on (for point-to-point, there is no Inverse ARP). IP split horizon checking is disabled by default for Frame Relay encapsulation, so routing updates come in and out the same interface. The routers learn the data-link connection identifiers (DLCIs) they need to use from the Frame Relay switch via LMI updates. The routers then Inverse ARP for the remote IP address and create a mapping of local DLCIs and their associated remote IP addresses.
Spicey |
---|
Spicey#show running-config Building configuration... Current configuration : 1705 bytes ! version 12.1 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname Spicey ! ! ! interface Ethernet0 ip address 124.124.124.1 255.255.255.0 ! interface Serial0 ip address 3.1.3.1 255.255.255.0 encapsulation frame-relay frame-relay interface-dlci 140 ! ! router rip network 3.0.0.0 network 124.0.0.0 ! line con 0 exec-timeout 0 0 transport input none line aux 0 line vty 0 4 login ! end |
Prasit |
---|
Prasit#show running-config Building configuration... Current configuration : 1499 bytes ! version 12.1 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname Prasit ! ! ! interface Ethernet0 ip address 123.123.123.1 255.255.255.0 ! ! interface Serial1 ip address 3.1.3.2 255.255.255.0 encapsulation frame-relay frame-relay interface-dlci 150 ! ! router rip network 3.0.0.0 network 123.0.0.0 ! ! ! line con 0 exec-timeout 0 0 transport input none line aux 0 line vty 0 4 login ! end |
驗證
-
show frame-relay map
-
show frame-relay pvc
-
show frame-relay lmi
-
ping <device name>
-
show ip route
Spicey#show frame-relay map Serial0 (up): ip 3.1.3.2 dlci 140(0x8C,0x20C0), dynamic, broadcast,, status defined, active Spicey#show frame-relay pvc PVC Statistics for interface Serial0 (Frame Relay DTE) Active Inactive Deleted Static Local 1 0 0 0 Switched 0 0 0 0 Unused 0 0 0 0 DLCI = 140, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0 input pkts 83 output pkts 87 in bytes 8144 out bytes 8408 dropped pkts 0 in FECN pkts0 in BECN pkts 0 out FECN pkts 0 out BECN pkts0 in DE pkts 0 out DE pkts 0 out bcast pkts 41 out bcast bytes 3652 pvc create time 01:31:50, last time pvc status changed 01:28:28 Spicey#show frame-relay lmi LMI Statistics for interface Serial0 (Frame Relay DTE) LMI TYPE = CISCO Invalid Unnumbered info 0 Invalid Prot Disc 0 Invalid dummy Call Ref 0 Invalid Msg Type 0 Invalid Status Message 0 Invalid Lock Shift 0 Invalid Information ID 0 Invalid Report IE Len 0 Invalid Report Request 0 Invalid Keep IE Len 0 Num Status Enq. Sent 550 Num Status msgs Rcvd 552 Num Update Status Rcvd 0 Num Status Timeouts 0 Spicey#ping 123.123.123.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 123.123.123.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 36/36/40 ms Spicey#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 3.0.0.0/24 is subnetted, 1 subnets C 3.1.3.0 is directly connected, Serial0 124.0.0.0/24 is subnetted, 1 subnets C 124.124.124.0 is directly connected, Ethernet0 R 123.0.0.0/8 [120/1] via 3.1.3.2, 00:00:08, Serial0
Prasit#show frame-relay map Serial1 (up): ip 3.1.3.1 dlci 150(0x96,0x2460), dynamic, broadcast,, status defined, active Prasit#show frame-relay pvc PVC Statistics for interface Serial1 (Frame Relay DTE) Active Inactive Deleted Static Local 1 0 0 0 Switched 0 0 0 0 Unused 0 0 0 0 DLCI = 150, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1 input pkts 87 output pkts 83 in bytes 8408 out bytes 8144 dropped pkts 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 0 out bcast pkts 38 out bcast bytes 3464 pvc create time 01:34:29, last time pvc status changed 01:28:05 Prasit#show frame-relay lmi LMI Statistics for interface Serial1 (Frame Relay DTE) LMI TYPE = CISCO Invalid Unnumbered info 0 Invalid Prot Disc 0 Invalid dummy Call Ref 0 Invalid Msg Type 0 Invalid Status Message 0 Invalid Lock Shift 0 Invalid Information ID 0 Invalid Report IE Len 0 Invalid Report Request 0 Invalid Keep IE Len 0 Num Status Enq. Sent 569 Num Status msgs Rcvd 570 Num Update Status Rcvd 0 Num Status Timeouts 0 Prasit#ping 124.124.124.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 124.124.124.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 36/36/36 ms Prasit#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 3.0.0.0/24 is subnetted, 1 subnets C 3.1.3.0 is directly connected, Serial1 R 124.0.0.0/8 [120/1] via 3.1.3.1, 00:00:19, Serial1 123.0.0.0/24 is subnetted, 1 subnets C 123.123.123.0 is directly connected, Ethernet0