[CASE]CISCO CRS和Redback SE800 isis邻居无法建立
热1已有 1237 次阅读 2011-09-03 19:49
CRS和SE800对联，MTU均为默认值，SE800为1500，CRS为1514。
跑isis level-2,建立不起来邻居关系。
CRS报的log为
%ROUTING-ISIS-4-ERR_BAD_PDU_FORMAT : L2 LAN IIH received from
GigabitEthernet0/5/0/3.151 SNPA 0030.8813.4931 contains a format error:
Item at offset 0 within Restart TLV at packet offset 44 has a bad format
(bad length 1 (must be 3))
1.更改两段端口的MTU都为1600，建立不起来邻居关系。
2.更改两边端口MTU为1500，也是建立不起来邻居关系。
在默认MTU情况下的抓包结果在此略过。
初步分析结果：
CRS发给SE800的TLV是这样的 D3 03 00 00 00
SE800发给CRS的TLV是这样的 D3 01 00
CRS设备:
0xD3是TLV的code，十进制是211，代表Restart TLV。0x03代表长度有3byte。
SE800设备:
0xD3是TLV的code，十进制是211，也代表Restart TLV。0x01代表长度只有1byte
CRS看到SE800送过来的长度只有1byte，就认为错了,就扔了不处理。
明显是Restart TLV造成的，由此判断是两个厂商对这个TLV理解不同造成的。
那么查阅RFC看看这个TLV是如何定义的。
RFC5306规定在RA bit设置为1的时候，后两个字节必须包括。但没有说长度一定为3。
3.2. Restart TLV
A new TLV is defined to be included in IIH PDUs. The presence of
this TLV indicates that the sender supports the functionality defined
in this document and it carries flags that are used to convey
information during a (re)start. All IIHs transmitted by a router
that supports this capability MUST include this TLV.
Type 211
Length: Number of octets in the Value field (1 to (3 + ID Length))
Value
No. of octets
+-----------------------+
| Flags | 1
+-----------------------+
| Remaining Time | 2
+-----------------------+
| Restarting Neighbor ID| ID Length
+-----------------------+
Shand & Ginsberg Standards Track [Page 5]
RFC 5306 Restart Signaling for IS-IS October 2008
Flags (1 octet)
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| Reserved |SA|RA|RR|
+--+--+--+--+--+--+--+--+
RR - Restart Request
RA - Restart Acknowledgement
SA - Suppress adjacency advertisement
(Note: Remaining fields are required when the RA bit is set.)
Remaining Time (2 octets)
Remaining holding time (in seconds)
Restarting Neighbor System ID (ID Length octets)
The System ID of the neighbor to which an RA refers. Note:
Implementations based on earlier versions of this document may not
include this field in the TLV when the RA is set. In this case, a
router that is expecting an RA on a LAN circuit SHOULD assume that
the acknowledgement is directed at the local system.
解决方法：略过
跑isis level-2,建立不起来邻居关系。
CRS报的log为
%ROUTING-ISIS-4-ERR_BAD_PDU_FORMAT : L2 LAN IIH received from
GigabitEthernet0/5/0/3.151 SNPA 0030.8813.4931 contains a format error:
Item at offset 0 within Restart TLV at packet offset 44 has a bad format
(bad length 1 (must be 3))
1.更改两段端口的MTU都为1600，建立不起来邻居关系。
2.更改两边端口MTU为1500，也是建立不起来邻居关系。
在默认MTU情况下的抓包结果在此略过。
初步分析结果：
CRS发给SE800的TLV是这样的 D3 03 00 00 00
SE800发给CRS的TLV是这样的 D3 01 00
CRS设备:
0xD3是TLV的code，十进制是211，代表Restart TLV。0x03代表长度有3byte。
SE800设备:
0xD3是TLV的code，十进制是211，也代表Restart TLV。0x01代表长度只有1byte
CRS看到SE800送过来的长度只有1byte，就认为错了,就扔了不处理。
明显是Restart TLV造成的，由此判断是两个厂商对这个TLV理解不同造成的。
那么查阅RFC看看这个TLV是如何定义的。
RFC5306规定在RA bit设置为1的时候，后两个字节必须包括。但没有说长度一定为3。
3.2. Restart TLV
A new TLV is defined to be included in IIH PDUs. The presence of
this TLV indicates that the sender supports the functionality defined
in this document and it carries flags that are used to convey
information during a (re)start. All IIHs transmitted by a router
that supports this capability MUST include this TLV.
Type 211
Length: Number of octets in the Value field (1 to (3 + ID Length))
Value
No. of octets
+-----------------------+
| Flags | 1
+-----------------------+
| Remaining Time | 2
+-----------------------+
| Restarting Neighbor ID| ID Length
+-----------------------+
Shand & Ginsberg Standards Track [Page 5]
RFC 5306 Restart Signaling for IS-IS October 2008
Flags (1 octet)
0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| Reserved |SA|RA|RR|
+--+--+--+--+--+--+--+--+
RR - Restart Request
RA - Restart Acknowledgement
SA - Suppress adjacency advertisement
(Note: Remaining fields are required when the RA bit is set.)
Remaining Time (2 octets)
Remaining holding time (in seconds)
Restarting Neighbor System ID (ID Length octets)
The System ID of the neighbor to which an RA refers. Note:
Implementations based on earlier versions of this document may not
include this field in the TLV when the RA is set. In this case, a
router that is expecting an RA on a LAN circuit SHOULD assume that
the acknowledgement is directed at the local system.
解决方法：略过
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