认证考完已经过了很久了，由于工作原因，很多知识还没有整理出来。
之后会陆续把相应SP的东西整理出来，留作日后复习。

对于跨域MPLS VPN来说，Option1是最好部署的一种方案。
但这是建立在牺牲了扩展性的前提下。
不过仍然有运营商在用此种方案，原因很简单—如果需要跨域的VPN不多，那么这种方案是最好的选择。
我们常把Option1叫做背靠背（Back-to-Back），顾名思义，即两端配置基本一致。
在域间交换时，数据包是以IPV4的形式交换的；对于原理，我们可以简单理解为普通的CE与PE的方式。
完整阅读

由于最近处理一个静态BFD的问题。
在此贴出BFD的配置及相关的资源链接供大家参考。
关于相关BFD协议的内容和他的模式问题，本想用dynamips加12.2(33)SRC来做测试并抓包分析，但发现一配置BFD，模拟器就crash，先后更换了SRD，SRE及更换了NPE-G1和 NPE-G2，现象一样存在。毕竟只是模拟器呀。。。。。。

所以关于相关BFD的更进一步分析，只能等到手头有设备时直接SPAN了。

注：VRF下的静态BFD，只从12.2(33)SRC才开始支持，支持平台为7600和7200。
6500需要在12.2(33)SXI才支持。 完整阅读

As everyone knows, the NTP is sync clock protocol.
That knowledge less other protocol.
But there are some attention:
——————————————
1. When you config more than one server in customer network.
Please don’t use the same stratum.
Base on the stratum, refer to
http://www.cisco.com/en/US/docs/ios/netmgmt/command/reference/nm_10.html#wp1093957
If customer use same stratum, it would instability and lost sync.

2013-1-22 更新
There are two reason will lead NTP flapping(lost sync):
1. If you have 2 ntp servers this sort of behavour can happen if the ntp parameters from those servers are similar. This is likely if your peering to two N7Ks. Note also that “prefer” is not a priority selection on XR.
2. NTP version mismatch between V3 and V4

Refer to “Prefer” option, may solve this problem, in most of the case but this is not a 100% solution. If the time from the “preferred” source reaches the client earlier than other configured peers, it is taken to be authoritive and independent of the current time and offset. And we sync to it, but before the NTP client is synchronized to this preferred peer (which should take a few seconds in general or a maximum of 5 minutes), if time updates from other configured peers reach the NTP client, the clock selection algorithms are applied to all of these and we have all the time sources pass through the selection algorithms and NTP tunes the client’s time to some peer, considering the other factors of offset, sync distance and dispersion.

We do have more than 2 servers at the same stratum level, in the CASE, We should try using prefer option to see if we have no issues with time stabilities. But if we have the two servers almost at the same distance, even “prefer” option would not help much.

So it is advisable to to have one server per stratum level.

完整阅读

最近搞了一阵DHCPv6，稍微总结了下：

配置：

ipv6 dhcp pool test
 address prefix 2004::/64
 dns-server 2004::2
 domain-name cisco.com
!
interface FastEthernet0/0
 no ip address
 完整阅读

关于MTU，我在之前的文章《MPLS Basic <2>》里介绍过，但不是很详细，现在总结下，并把新的理解写出来，跟大家探讨。

我做了3个实验来测试MTU的具体含义。详细看以下实验及总结：

环境：

1. MPLS环境，注意没有VPN，因此只有1层标签（适合1-3）。
2. R1和R3分别设有环回口，用于测试，普通的环回口及地址，没有特殊配置。
完整阅读