Showing posts from September 30, 2007

Bidirectional Forwarding Detection(BFD)

Bidirectional Forwarding Detection (BFD) is a network protocol used to detect faults between two forwarding engines. It provides low-overhead detection of faults even on physical media that don't support failure detection of any kind, such as ethernet, virtual circuits, tunnels and MPLS LSPs.

BFD establishes a session between two endpoints over a particular link. If more than one link exists between two systems, multiple BFD sessions may be established to monitor each one of them. The session is established with a three-way handshake, and is torn down the same way. Authentication may be enabled on the session. A choice of simple password, MD5 or SHA1 authentication is available.

BFD does not have a discovery mechanism; sessions must be explicitly configured between endpoints. BFD may be used on many different underlying transport mechanisms and layers, and operates independently of all of these. Therefore, it needs to be encapsulated by whatever transport it uses. For example, monit…

Generalized MPLS(GMPLS)

Generalized MPLS

a. What is "Generalized MPLS" or "GMPLS"
From "Generalized Multi-Protocol Label Switching Architecture" "Generalized MPLS extends MPLS to encompass time-division (e.g. SONET ADMs), wavelength (optical lambdas) and spatial switching (e.g. incoming port or fiber to outgoing port or fiber)."

GMPLS represents a natural extension of MPLS to allow MPLS to be used as the control mechanism for configuring not only packet-based paths, but also paths in non-packet based devices such as optical switches, TDM muxes, and SONET/ADMs.

For an overview of GMPLS, see Generalized Multiprotocol Label Switching: An Overview of Routing and Management Enhancements

b. What are the components of GMPLS?
GMPLS introduces a new protocol called the "Link Management Protocol" or LMP. LMP runs between adjacent nodes and is responsible for establishing control channel connectivity as well as failure detection. LMP also verifies connectivity between ch…


IPv6相較於IPv4的改革,除了IP Address數量之外,還有一個很重要的就是取消了IPv4的broadcast,全部改為Multicast及新增加的Anycast來取代,以下是目前IANA所定義的一些multicast address,雖然不用強記,但是對於了解IPv6的運作肯定會有所幫助!


(last updated 2007-08-30)

IPv6 multicast addresses are defined in "IP Version 6 Addressing
Architecture" [RFC4291]. This defines fixed scope and variable scope
multicast addresses.

IPv6 multicast addresses are distinguished from unicast addresses by the
value of the high-order octet of the addresses: a value of 0xFF (binary
11111111) identifies an address as a multicast address; any other value
identifies an address as a unicast address.

The rules for assigning new IPv6 multicast addresses are defined in
[RFC3307]. IPv6 multicast addresses not listed below are reserved.

Current IPv6 multicast addresses are listed below.

Fixed Scope Multicast Addresses

These permanently assigned multicast addresses are valid over a specified
scope value.

Node-Local Scope

Cisco Nonstop Forwarding for BGP: Deployment & Troubleshooting


When the NSF-capable router performs a route processor switchover, the TCP connection to the Peer Router is cleared; a Peer Router that does not support BGP restart then clears all routes associated with the Restarting Router and no longer forwards packets to it. With BGP Graceful Restart, the Peer Router marks all routes to the Restarting Router as stale, but continues to use them for packet forwarding, based upon the knowledge that the Restarting Router will re-establish the BGP session shortly and that it maintains the capability to forward packets in the interim.

When the Restarting Router's newly active RP opens the new BGP session, it will again send the Graceful Restart capability (#64). However, this time, the restart bit in the Restart Flags portion of the capability exchange will be set. This notifies the Peer Routers that the restart of the BGP process on the Restarting Router caused the disconnect/reconnect.

While continuing to forward packets, the Peer Router refresh…

RFC 4364 - BGP/MPLS IP Virtual Private Networks (VPNs)(About Route Distinguisher)

4.1. The VPN-IPv4 Address Family

The BGP Multiprotocol Extensions [BGP-MP] allow BGP to carry routes
from multiple "address families". We introduce the notion of the
"VPN-IPv4 address family". A VPN-IPv4 address is a 12-byte quantity,
beginning with an 8-byte Route Distinguisher (RD) and ending with a
4-byte IPv4 address. If several VPNs use the same IPv4 address
prefix, the PEs translate these into unique VPN-IPv4 address
prefixes. This ensures that if the same address is used in several
different VPNs, it is possible for BGP to carry several completely
different routes to that address, one for each VPN.

Since VPN-IPv4 addresses and IPv4 addresses are different address
families, BGP never treats them as comparable addresses.

An RD is simply a number, and it does not contain any inherent
information; it does not identify the origin of the route or the set
of VPNs to which the route is to be distributed. The purpose of the
RD is sol…

A Brief Overview of SONET Technology

最近開始逐步準備SP(Service Provider) CCIE Written,因此我將會把相關準備方向及參考資料放上來供大家參考,準備CCIE Written很大的困擾就是不知道要看什麼書籍…因為出題範圍就是…幾近沒有範圍(比以前CCIE沒有分類前好一些而已),所以只好針對一些有可能的方向找出重點來了解,順便可以提昇自己的知識領域:

SONET Basics
SONET defines optical signals and a synchronous frame structure for multiplexed digital traffic. It is a set of standards that define the rates and formats for optical networks specified in ANSI T1.105, ANSI T1.106, and ANSI T1.117.

A similar standard, Synchronous Digital Hierarchy (SDH), is used in Europe by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). SONET equipment is generally used in North America, and SDH equipment is generally accepted everywhere else in the world.

Both SONET and SDH are based on a structure that has a basic frame format and speed. The frame format used by SONET is the Synchronous Transport Signal (STS), with STS-1 as the base-level signal at 51.84 Mbps. An STS-1 frame can be carried in an OC-1 signal. The frame format used by SDH is th…

Cisco (CSCO) today 100 times bigger than 3Com (COMS) -- it wasn't in 1994

This morning 3Com (NASDAQ: COMS) announced that private equity firm, Bain Capital, would put it out of its misery and pay $2.2 billion in cash for the company. 3Com has lagged so far behind that it has been painful to watch. 3Com and Cisco Systems (NASDAQ: CSCO) indeed could provide at least two to three chapters in an investing teaching and history book. Here's the CliffsNotes version:

Summer of 1994 was a tough technology environment. Technology had a great run from 1990 through 1994, till summer that is. Valuations contracted and investor fatigue set in for about four to five months. I was traveling through Silicon Valley with a couple of British portfolio managers visiting companies. One day we had a breakfast meeting with then CEO Eric Benamou of 3Com and lunch with a senior VP at Cisco (whose name escapes me). Benamou was an intellectual, a refined man, but did not possess the street smarts necessary for a tech company CEO. He was arrogant and bluntly declared that Cisco'…