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The MOVE Fire

This is a personal recollection on the Move fire on May 13, 1985 Philadelphia police fired thousands of rounds at the MOVE house, city officials approved dropping an explosive device on the roof, the resulting fire was allowed to burn, 11 people—including five children—died, and 61 homes were destroyed. Philadelphia City Council later called it a “brutal attack carried out by the City of Philadelphia on its own citizens” and acknowledged that no individual faced criminal consequences for the bombing. One timeline correction worth preserving for the BHP record: the major previous MOVE-police confrontation was August 8, 1978, about seven years before the bombing, not a year or two earlier. Officer James Ramp was killed, other police and firefighters were wounded, nine MOVE members were later convicted, and television cameras recorded police beating Delbert Africa during his arrest. The 1985 MOVE Commission later specifically criticized city planners for failing to adequately use lessons from that 1978 confrontation. And that actually strengthens the point you’re making: 1985 did not happen without precedent or institutional memory. There had already been a deadly confrontation with MOVE, years of conflict, negotiations and police involvement before Osage Avenue.

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BLACK FACTS
The Truths They Never Taught You...

The Violence That Helped Spark the NAACP

In August 1908, a white mob attacked Springfield, Illinois’s Black community, destroying homes and businesses and lynching two Black men. National outrage over the violence helped spur the movement that created the NAACP the following year.

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Wikipedia

Generic routing encapsulation

Generic routing encapsulation
Communication protocol
PurposeNetwork tunneling
DeveloperCisco Systems
Introduction1994[1]
RFCs1701, 1702, 2784

Generic routing encapsulation (GRE) is a tunneling protocol developed by Cisco Systems that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links or point-to-multipoint links over an Internet Protocol network.[2]

Example uses

[edit]
  • In conjunction with PPTP to create VPNs.
  • In conjunction with IPsec VPNs to allow passing of routing information between connected networks.
  • In mobility management protocols.
  • In A8/A10 interfaces to encapsulate IP data to/from Packet Control Function (PCF).
  • Linux and BSD can establish ad-hoc IP over GRE tunnels which are interoperable with Cisco equipment.
  • Distributed denial of service (DDoS) protected appliance to an unprotected endpoint.

Example protocol stack

[edit]
OSI model layer Protocol example
7. Application HTTP
4. Transport TCP
3. Network (GRE-encapsulated) IPv4
Encapsulation GRE
3. Network IPv6
2. Data link Ethernet
1. Physical Ethernet physical layer

Based on the principles of protocol layering in OSI, protocol encapsulation, not specifically GRE, breaks the layering order. It may be viewed as a separator between two different protocol stacks, one acting as a carrier for another.

Delivery protocols

[edit]

GRE packets that are encapsulated within IP directly, use IP protocol type 47 in the IPv4 header's Protocol field[3] or the IPv6 header's Next Header field.[4]

For performance reasons, GRE can also be encapsulated in UDP packets.[5] Better throughput may be achieved by using Equal-cost multi-path routing.

Packet header

[edit]

Extended GRE packet header (RFC 2890)

[edit]

The extended version of the GRE packet header[6] is represented below:

Extended GRE header format
Offsets Octet 0 1 2 3
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 C K S Reserved 0 Version Protocol Type
4 32 Checksum (optional) Reserved 1 (optional)
8 64 Key (optional)
12 96 Sequence Number (optional)
C (1 bit)
Checksum bit. Set to 1 if a checksum is present.
K (1 bit)
Key bit. Set to 1 if a key is present.
S (1 bit)
Sequence number bit. Set to 1 if a sequence number is present.
Reserved 0 (9 bits)
Reserved bits; set to 0.
Version (3 bits)
GRE Version number; set to 0.
Protocol Type (16 bits)
Indicates the ether protocol type of the encapsulated payload. (For IPv4, this would be hex 0800.)
Checksum (16 bits)
Present if the C bit is set; contains the checksum for the GRE header and payload.
Reserved 1 (16 bits)
Present if the C bit is set; is set to 0.
Key (32 bits)
Present if the K bit is set; contains an application-specific key value.
Sequence Number (32 bits)
Present if the S bit is set; contains a sequence number for the GRE packet.

Standard GRE packet header (RFC 2784)

[edit]

A standard GRE packet header structure[7] is represented in the diagram below.

Standard GRE header format
Offsets Octet 0 1 2 3
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 C Reserved 0 Version Protocol Type
4 32 Checksum (optional) Reserved 1 (optional)
C (1 bit)
Checksum bit. Set to 1 if a checksum is present.
Reserved 0 (12 bits)
Reserved bits; set to 0.
Version (3 bits)
GRE Version number; set to 0.
Protocol Type (16 bits)
Indicates the ether protocol type of the encapsulated payload. (For IPv4, this would be hexadecimal 0x0800; for IPv6, it would be 0x86DD.[4])
Checksum (16 bits)
Present if the C bit is set; contains the checksum for the GRE header and payload.
Reserved 1 (16 bits)
Present if the C bit is set; its contents is set to 0.

Original GRE packet header (RFC 1701)

[edit]

The newer structure superseded the original structure:[1]

Original GRE header format
Offsets Octet 0 1 2 3
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 C R K S s Recur Flags Version Protocol Type
4 32 Checksum (optional) Offset (optional)
8 64 Key (optional)
12 96 Sequence Number (optional)
16 128 Routing (optional, variable length)

The original GRE RFC defined further fields in the packet header which became obsolete in the current standard:

C (1 bit)
Checksum bit. Set to 1 if a checksum is present.
R (1 bit)
Routing Bit. Set to 1 if Routing and Offset information are present.
K (1 bit)
Key bit. Set to 1 if a key is present.
S (1 bit)
Sequence number bit. Set to 1 if a sequence number is present.
s (1 bit)
Strict source route bit.
Recur (3 bits)
Recursion control bits.
Flags (5 bits)
Reserved for future use, set to 0.
Version (3 bits)
Set to 0.
Protocol Type (16 bits)
Indicates the ether protocol type of the encapsulated payload.
Checksum (16 bits)
Present if the C bit is set; contains the checksum for the GRE header and payload.
Offset (16 bits)
Present if R bit or C bit is set; contains valid information, only if R bit is set. An offset field indicating the offset within the Routing field to the active source route entry.
Key (32 bits)
Present if the K bit is set; contains an application-specific key value.
Sequence Number (32 bits)
Present if the S bit is set; contains a sequence number for the GRE packet.
Routing (variable)
Present if R bit is set; contains a list of source route entries, therefore is of variable length.

PPTP GRE packet header

[edit]

The Point-to-Point Tunneling Protocol (PPTP) [8] uses a variant GRE packet header structure, represented below. PPTP creates a GRE tunnel through which the PPTP GRE packets are sent.

PPTP GRE header format
Offsets Octet 0 1 2 3
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 C R K S s Recur A Flags Version Protocol Type
4 32 Key Payload Length Key Call ID
8 64 Sequence Number (optional)
12 96 Acknowledgement Number (optional)
C (1 bit)
Checksum bit. For PPTP GRE packets, this is set to 0.
R (1 bit)
Routing bit. For PPTP GRE packets, this is set to 0.
K (1 bit)
Key bit. For PPTP GRE packets, this is set to 1. (All PPTP GRE packets carry a key.)
S (1 bit)
Sequence number bit. Set to 1 if a sequence number is supplied, indicating a PPTP GRE data packet.
s (1 bit)
Strict source route bit. For PPTP GRE packets, this is set to 0.
Recur (3 bits)
Recursion control bits. For PPTP GRE packets, these are set to 0.
A (1 bit)
Acknowledgment number present. Set to 1 if an acknowledgment number is supplied, indicating a PPTP GRE acknowledgment packet.
Flags (4 bits)
Flag bits. For PPTP GRE packets, these are set to 0.
Version (3 bits)
GRE Version number. For PPTP GRE packets, this is set to 1.
Protocol Type (16 bits)
For PPTP GRE packets, this is set to hex 880B.
Key Payload Length (16 bits)
Contains the size of the payload, not including the GRE header.
Key Call ID (16 bits)
Contains the Peer's Call ID for the session to which the packet belongs.
Sequence Number (32 bits)
Present if the S bit is set; contains the GRE payload sequence number.
Acknowledgement Number (32 bits)
Present if the A bit is set; contains the sequence number of the highest GRE payload packet received by the sender.

Standards

[edit]
  • RFC 1701: Generic Routing Encapsulation (GRE) (informational)
  • RFC 1702: Generic Routing Encapsulation over IPv4 networks (informational)
  • RFC 2637: Point to Point Tunneling Protocol (informational)
  • RFC 2784: Generic Routing Encapsulation (GRE) (proposed standard, updated by RFC 2890)
  • RFC 2890: Key and Sequence Number Extensions to GRE (proposed standard)
  • RFC 8086: GRE-in-UDP Encapsulation (proposed standard)

See also

[edit]

References

[edit]
  1. ^ a b S. Hanks; T. Li; D. Farinacci; P. Traina (October 1994). Generic Routing Encapsulation (GRE). Network Working Group. doi:10.17487/RFC1701. RFC 1701. Informational.
  2. ^ US 7801021B1, Nikolaos Triantafillis; Robert J. Ordemann & Simon D. Barber, "Generic routing encapsulation tunnel keepalives", issued 2010-09-21, assigned to Cisco Technology Inc. 
  3. ^ S. Hanks; T. Li; D. Farinacci; P. Traina (October 1994). Generic Routing Encapsulation over IPv4 networks. Network Working Group. doi:10.17487/RFC1702. RFC 1702. Informational.
  4. ^ a b C. Pignataro; R. Bonica; S. Krishnan (October 2015). IPv6 Support for Generic Routing Encapsulation (GRE). Internet Engineering Task Force. doi:10.17487/RFC7676. ISSN 2070-1721. RFC 7676. Proposed Standard.
  5. ^ E. Crabbe; E. Crabbet; T. Herbert (March 2017). L. Yong (ed.). GRE-in-UDP Encapsulation. Internet Engineering Task Force. doi:10.17487/RFC8086. ISSN 2070-1721. RFC 8086. Proposed Standard.
  6. ^ G. Dommety (September 2000). Key and Sequence Number Extensions to GRE. Network Working Group. doi:10.17487/RFC2890. RFC 2890. Proposed Standard.
  7. ^ D. Farinacci; T. Li; S. Hanks; D. Meyer; P. Traina (March 2000). Generic Routing Encapsulation (GRE). Network Working Group. doi:10.17487/RFC2784. RFC 2784. Proposed Standard. Updated by RFC 2890.
  8. ^ K. Hamzeh; G. Pall; W. Verthein; J. Taarud; W. Little; G. Zorn (July 1999). Point-to-Point Tunneling Protocol (PPTP). Network Working Group. doi:10.17487/RFC2637. RFC 2637. Informational.
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Wikipedia

Generic routing encapsulation

Generic routing encapsulation (GRE) is a tunneling protocol developed by Cisco Systems that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links or point-to-multipoint links over an Internet Protocol network.

MORE →
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Wikipedia

Network Virtualization using Generic Routing Encapsulation

Network Virtualization using Generic Routing Encapsulation (NVGRE) is a network virtualization technology that attempts to alleviate the scalability problems associated with large cloud computing deployments. It uses Generic Routing Encapsulation (GRE) to tunnel layer 2 packets over layer 3 networks. Its principal backer is Microsoft.

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Point-to-Point Tunneling Protocol

The Point-to-Point Tunneling Protocol (PPTP) is an obsolete method for implementing virtual private networks. PPTP has many well known security issues. PPTP uses a TCP control channel and a Generic Routing Encapsulation tunnel to encapsulate PPP packets. Many modern VPNs use various forms of UDP for this same functionality. The PPTP specification does not describe encryption or authentication features and relies on the Point-to-Point Protocol being tunneled to implement any and all security functionalities. The PPTP implementation that ships with the Microsoft Windows product families implements various levels of authentication and encryption natively as standard features of the Windows PPTP stack. The intended use of this protocol is to provide security levels and remote access levels comparable with typical VPN products.

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Wikipedia

Generic Stream Encapsulation

Generic Stream Encapsulation, or GSE for short, is a data link layer protocol defined by DVB. GSE provides means to carry packet oriented protocols such as IP on top of uni-directional physical layers such as DVB-S2, DVB-T2 and DVB-C2. GSE provides additional features beyond the pure carriage of IP datagrams that increase the protocol flexibility and applicability. Some key GSE functions/characteristics are: Support for multi-protocol encapsulation (IPv4, IPv6, MPEG, ATM, Ethernet, 802.1pQ VLANs, etc.) Transparency to network layer functions, including IP encryption and IP header compression. Support of several addressing modes. In addition to the 6-byte MAC address (including multicast and unicast), it supports a MAC address-less mode, and an optional 3-byte address mode. A mechanism for fragmenting IP datagrams or other network layer packets over Base Band frames to support ACM/VCM. Support for hardware filtering. Extensibility: additional link protocols can be included through specific protocol type values (e.g. Layer 2 security, IP Header Compression, etc.).

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TOPIC OF THE DAY

Greenwood / Black Wall Street

Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.

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TRIVIA QUESTION OF THE DAY

Which Black woman became the first elected to the United States Congress?

Shirley Chisholm, elected in 1968.